README.md

# clean-code-javascript

## Kazalo vsebine 

1. [Uvod](#uvod)
2. [Spremenljivke](#spremenljivke)
3. [Funkcije](#funkcije)
4. [Objekti in podatkovne strukture](#objekti-in-podatkovne-strukture)
5. [Razredi](#classes)
6. [SOLID](#solid)
7. [Testiranje](#testiranje)
8. [Asinhronost](#asinhronost)
9. [Ravnanje z napakami](#ravnanje-z-napakami)
10. [Oblikovanje](#oblikovanje)
11. [Komentarji](#komentarji)
12. [Prevanjanje](#prevajanje)

## Uvod

![Humoristična podoba ocenjevanja kakovosti programske opreme kot štetje števila izrečenih vzklikov med branjem kode](https://www.osnews.com/images/comics/wtfm.jpg)
<br>
Načela programskega inženiringa iz knjige Roberta C. Martina
[_Clean Code_](https://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882),
prilagojena za JavaScript. To ni slogovni vodnik. To je vodnik za pisanje
[berljive, ponovno uporabne in ponovljive](https://github.com/ryanmcdermott/3rs-of-software-architecture) kode v jeziku JavaScript.

Ni potrebno, da vse principe, kateri so opisani v vodiču natančno upoštevate. 
Ta vodič velja za smernice katere so avtorji knjige _Clean Code_ napisali na podlagi 
dolgoletnih kolektivnih izkušenj.

Naša stroka inženiringa programske opreme je stara le nekaj več kot 50 let, 
mi pa se iz nje lahko še veliko naučimo. Ko bo arhitektura programske opreme 
stara toliko kot arhitektura sama, bomo morda imeli boljša pravila, katera bi 
morali upoštevati. Za zdaj naj te smernice služijo kot merilo, po katerem lahko 
ocenimo kakovost JavaScript kode, ki jo ustvarjate vi in vaša ekipa.

Samo še nekaj: če boste poznali smernice iz tega vodiča, ne boste takoj 
postali boljši programer, tudi več letno delo z njimi ne pomeni, da ne boste delali
več napak. Vsak kos kode se začne kot grobi osnutek, kot kos mokre gline, ki dobi 
svojo končno obliko. Na koncu z dletom odstranimo nepravilnosti, ko pregledamo kodo 
s sodelavci. Ne obremenjujte se s prvimi osnutki kode, ki potrebujejo
izboljšave!


## **Spremenljivke**

### Uporabite smiselna in izgovorljiva imena spremenljivk

**Slabo:**

```javascript
const yyyymmdstr = moment().format("YYYY/MM/DD");
```

**Dobro:**

```javascript
const currentDate = moment().format("YYYY/MM/DD");
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Uporabite isto besedišča za isto vrsto spremenljivke

**Slabo:**

```javascript
getUserInfo();
getClientData();
getCustomerRecord();
```

**Dobro:**

```javascript
getUser();
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Uporabite imena, katere boste kasneje brez napora našli

Med kodiranjem boste prebrali več kode, kot je boste kadarkoli napisali. Pomembno je, 
da je vaša koda berljiva in jo je mogoče iskati s funkcijo za iskanje v razvijalskemu programu.
Če spremenljivk ustrezno ne poimenujte ali jih nesmisleno poimenujete, s tem škodite bralcu vaše kode. 
Imena naj bodo primerna za iskanje.
[buddy.js](https://github.com/danielstjules/buddy.js) in
[ESLint](https://github.com/eslint/eslint/blob/660e0918933e6e7fede26bc675a0763a6b357c94/docs/rules/no-magic-numbers.md)
vam lahko pomagata prepoznati neimenovane konstante.

**Slabo:**

```javascript
// Za kaj za vraga je 86400000?
setTimeout(blastOff, 86400000);
```

**Dobro:**

```javascript
// Deklarirajte jih kot konstante z velikimi črkami.
const MILLISECONDS_PER_DAY = 60 * 60 * 24 * 1000; //86400000;

setTimeout(blastOff, MILLISECONDS_PER_DAY);
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Uporaba pojasnjevalnih spremenljivk

**Slabo:**

```javascript
const address = "One Infinite Loop, Cupertino 95014";
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
saveCityZipCode(
  address.match(cityZipCodeRegex)[1],
  address.match(cityZipCodeRegex)[2]
);
```

**Dobro:**

```javascript
const address = "One Infinite Loop, Cupertino 95014";
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
const [_, city, zipCode] = address.match(cityZipCodeRegex) || [];
saveCityZipCode(city, zipCode);
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Izogibajte se miselnim zemljevidom

Eksplicitno je bolje kot implicitno.

**Slabo:**

```javascript
const lokacije = ["Austin", "New York", "San Francisco"];
locations.forEach(l => {
  doStuff();
  doSomeOtherStuff();
  // ...
  // ...
  // ...
  // Torej kaj je že 'l'?
  dispatch(l);
});
```

**Dobro:**

```javascript
const locations = ["Austin", "New York", "San Francisco"];
locations.forEach(location => {
  doStuff();
  doSomeOtherStuff();
  // ...
  // ...
  // ...
  dispatch(location);
});
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Ne dodajajte nepotrebnega konteksta

Če vam ime razreda/objekta nekaj pove, tega ne ponavljajte v svojem imenu spremenljivke.

**Slabo:**

```javascript
const Car = {
  carMake: "Honda",
  carModel: "Accord",
  carColor: "Blue"
};

function paintCar(car, color) {
  car.carColor = color;
}
```

**Dobro:**

```javascript
const Car = {
  make: "Honda",
  model: "Accord",
  color: "Blue"
};

function paintCar(car, color) {
  car.color = color;
}
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Uporabite privzete vrednosti

**Slabo:**

```javascript
function createMicrobrewery(name) {
  const breweryName = name || "Hipster Brew Co.";
  // ...
}
```

**Dobro:**

```javascript
function createMicrobrewery(name = "Hipster Brew Co.") {
  // ...
}
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

## **Funkcije**

### Argumenti funkcije (2 ali manj v idelanem primeru)

Omejitev števila parametrov funkcije je izjemno pomembna, saj
olajša testiranje funkcije. Če imate več kot tri argumente, boste imeli težave saj
boste morali testirati na tone različnih primerov z vsakim argumentom funkcije.

Idealno je, da uporabite en ali dva argumenta, trem pa se je potrebno izogibati, če je 
le mogoče. Če morate uporabiti več kot dva argumenta, potem funkcija poskuša 
narediti preveč. V primerih kjer se vam zdi, da potrebujete več argumentov, JavaScript 
omogoča enostavno ustvarjanje objektov, ki jih lahko nato 
uporabite kot argument v funkciji.

Da bi bilo jasno, katere lastnosti funkcija pričakuje, lahko uporabite ES2015/ES6
sintakso destrukturiranja. Prednosti so:
   
1. Iz funkcije je takoj razvidno, katere lastnosti uporablja.
2. Uporablja se lahko za simulacijo poimenovanih parametrov.
3. Destrukturiranje klonira tudi določene primitivne vrednosti argumenta predmeta, 
   posredovanega v funkcijo. To lahko pomaga preprečiti stranske učinke. 
   Opomba: predmeti in polja, ki so destrukturirani iz objekta argumenta, SE NE klonirajo.
4. Linter vas lahko opozori na neuporabljene lastnosti, kar bi bilo brez 
   destrukturiranja nemogoče.

**Slabo:**

```javascript
function createMenu(title, body, buttonText, cancellable) {
  // ...
}

createMenu("Foo", "Bar", "Baz", true);

```

**Dobro:**

```javascript
function createMenu({ title, body, buttonText, cancellable }) {
  // ...
}

createMenu({
  title: "Foo",
  body: "Bar",
  buttonText: "Baz",
  cancellable: true
});
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Funkcije naj delajo samo eno stvar na enkrat

Verjetno najpomembnejše pravilo kodiranja. Ko funkcije počnejo več kot eno stvar, 
jih boste težje sestavii, preizkusili in jih utemeljili. Če lahko funkcijo izolirate 
na eno samo dejanje, jo je mogoče zlahka preoblikovati, hkrati pa bo vaša koda čistejša za branje. 
Če iz tega vodiča ne odnesete ničesar drugega, se držite tega pravila!

**Slabo:**

```javascript
function emailClients(clients) {
  clients.forEach(client => {
    const clientRecord = database.lookup(client);
    if (clientRecord.isActive()) {
      email(client);
    }
  });
}
```

**Dobro:**

```javascript
function emailActiveClients(clients) {
  clients.filter(isActiveClient).forEach(email);
}

function isActiveClient(client) {
  const clientRecord = database.lookup(client);
  return clientRecord.isActive();
}
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Ime funkcije naj pojasnjuje za kaj so zadolžene

**Slabo:**

```javascript
function addToDate(date, month) {
  // ...
}

const date = new Date();

// Iz imena funkcije je težko razvidno za kaj je zadolžena
addToDate(date, 1);
```

**Dobro:**

```javascript
function addMonthToDate(month, date) {
  // ...
}

const date = new Date();
addMonthToDate(1, date);
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Funkcije naj imajo samo eno raven abstraktnosti

Kadar imate več kot eno raven abstrakcije, funkcija običajno počne preveč. 
Razdelitev funkcij omogoča ponovno uporabnost in lažjo testiranje.

**Slabo:**

```javascript
function parseBetterJSAlternative(code) {
  const REGEXES = [
    // ...
  ];

  const statements = code.split(" ");
  const tokens = [];
  REGEXES.forEach(REGEX => {
    statements.forEach(statement => {
      // ...
    });
  });

  const ast = [];
  tokens.forEach(token => {
    // lex...
  });

  ast.forEach(node => {
    // parse...
  });
}
```

**Dobro:**

```javascript
function parseBetterJSAlternative(code) {
  const tokens = tokenize(code);
  const syntaxTree = parse(tokens);
  syntaxTree.forEach(node => {
    // parse...
  });
}

function tokenize(code) {
  const REGEXES = [
    // ...
  ];

  const statements = code.split(" ");
  const tokens = [];
  REGEXES.forEach(REGEX => {
    statements.forEach(statement => {
      tokens.push(/* ... */);
    });
  });

  return tokens;
}

function parse(tokens) {
  const syntaxTree = [];
  tokens.forEach(token => {
    syntaxTree.push(/* ... */);
  });

  return syntaxTree;
}
```

**[⬆ Nazaj na vrh](#kazalo-vsebine)**

### Odstranite podvojeno kodo

Po najboljših močeh se izogibajte podvojeni kodi. Podvojena koda je slaba,
saj pomeni, da je v kodi več kot eno mesto, na katerem boste morali narediti spremembo.

Predstavljajte si, da vodite restavracijo in spremljate zalogo:
paradižnik, čebulo, česen, začimbe itd. Če imate več seznamov, s katerimi vodite zalogo
boste morali posodobiti vse, takoj ko postrežete jed z npr. paradižnikom. 
Če imate samo en seznam, ga boste morali posodobiti samo na enem mestu!

Oftentimes you have duplicate code because you have two or more slightly
different things, that share a lot in common, but their differences force you
to have two or more separate functions that do much of the same things. Removing
duplicate code means creating an abstraction that can handle this set of
different things with just one function/module/class.

Pogosto kodo podvajamo na mestih kjer imamo , ki imajo veliko 
skupnega med sabo, njihove razlike pa vas prisilijo <-- //TODO

Pogosto se koda podvaja, ker imate dve ali več rahlo ali več različnih stvari, ki imajo veliko skupnega, vendar vas njihove razlike prisilijo, da da bi morali imeti dve ali več ločenih funkcij, ki počnejo večinoma iste stvari. Odstranjevanje podvojene kode pomeni ustvariti abstrakcijo, ki lahko obravnava ta sklop različnih stvari z eno samo funkcijo/modulom/razredom.

Getting the abstraction right is critical, that's why you should follow the
SOLID principles laid out in the _Classes_ section. Bad abstractions can be
worse than duplicate code, so be careful! Having said this, if you can make
a good abstraction, do it! Don't repeat yourself, otherwise you'll find yourself
updating multiple places anytime you want to change one thing.

**Bad:**

```javascript
function showDeveloperList(developers) {
  developers.forEach(developer => {
    const expectedSalary = developer.calculateExpectedSalary();
    const experience = developer.getExperience();
    const githubLink = developer.getGithubLink();
    const data = {
      expectedSalary,
      experience,
      githubLink
    };

    render(data);
  });
}

function showManagerList(managers) {
  managers.forEach(manager => {
    const expectedSalary = manager.calculateExpectedSalary();
    const experience = manager.getExperience();
    const portfolio = manager.getMBAProjects();
    const data = {
      expectedSalary,
      experience,
      portfolio
    };

    render(data);
  });
}
```

**Good:**

```javascript
function showEmployeeList(employees) {
  employees.forEach(employee => {
    const expectedSalary = employee.calculateExpectedSalary();
    const experience = employee.getExperience();

    const data = {
      expectedSalary,
      experience
    };

    switch (employee.type) {
      case "manager":
        data.portfolio = employee.getMBAProjects();
        break;
      case "developer":
        data.githubLink = employee.getGithubLink();
        break;
    }

    render(data);
  });
}
```

**[⬆ back to top](#table-of-contents)**

### Set default objects with Object.assign

**Bad:**

```javascript
const menuConfig = {
  title: null,
  body: "Bar",
  buttonText: null,
  cancellable: true
};

function createMenu(config) {
  config.title = config.title || "Foo";
  config.body = config.body || "Bar";
  config.buttonText = config.buttonText || "Baz";
  config.cancellable =
    config.cancellable !== undefined ? config.cancellable : true;
}

createMenu(menuConfig);
```

**Good:**

```javascript
const menuConfig = {
  title: "Order",
  // User did not include 'body' key
  buttonText: "Send",
  cancellable: true
};

function createMenu(config) {
  let finalConfig = Object.assign(
    {
      title: "Foo",
      body: "Bar",
      buttonText: "Baz",
      cancellable: true
    },
    config
  );
  return finalConfig
  // config now equals: {title: "Order", body: "Bar", buttonText: "Send", cancellable: true}
  // ...
}

createMenu(menuConfig);
```

**[⬆ back to top](#table-of-contents)**

### Don't use flags as function parameters

Flags tell your user that this function does more than one thing. Functions should do one thing. Split out your functions if they are following different code paths based on a boolean.

**Bad:**

```javascript
function createFile(name, temp) {
  if (temp) {
    fs.create(`./temp/${name}`);
  } else {
    fs.create(name);
  }
}
```

**Good:**

```javascript
function createFile(name) {
  fs.create(name);
}

function createTempFile(name) {
  createFile(`./temp/${name}`);
}
```

**[⬆ back to top](#table-of-contents)**

### Avoid Side Effects (part 1)

A function produces a side effect if it does anything other than take a value in
and return another value or values. A side effect could be writing to a file,
modifying some global variable, or accidentally wiring all your money to a
stranger.

Now, you do need to have side effects in a program on occasion. Like the previous
example, you might need to write to a file. What you want to do is to
centralize where you are doing this. Don't have several functions and classes
that write to a particular file. Have one service that does it. One and only one.

The main point is to avoid common pitfalls like sharing state between objects
without any structure, using mutable data types that can be written to by anything,
and not centralizing where your side effects occur. If you can do this, you will
be happier than the vast majority of other programmers.

**Bad:**

```javascript
// Global variable referenced by following function.
// If we had another function that used this name, now it'd be an array and it could break it.
let name = "Ryan McDermott";

function splitIntoFirstAndLastName() {
  name = name.split(" ");
}

splitIntoFirstAndLastName();

console.log(name); // ['Ryan', 'McDermott'];
```

**Good:**

```javascript
function splitIntoFirstAndLastName(name) {
  return name.split(" ");
}

const name = "Ryan McDermott";
const newName = splitIntoFirstAndLastName(name);

console.log(name); // 'Ryan McDermott';
console.log(newName); // ['Ryan', 'McDermott'];
```

**[⬆ back to top](#table-of-contents)**

### Avoid Side Effects (part 2)

In JavaScript, some values are unchangeable (immutable) and some are changeable 
(mutable). Objects and arrays are two kinds of mutable values so it's important 
to handle them carefully when they're passed as parameters to a function. A 
JavaScript function can change an object's properties or alter the contents of 
an array which could easily cause bugs elsewhere.

Suppose there's a function that accepts an array parameter representing a 
shopping cart. If the function makes a change in that shopping cart array - 
by adding an item to purchase, for example - then any other function that 
uses that same `cart` array will be affected by this addition. That may be 
great, however it could also be bad. Let's imagine a bad situation:

The user clicks the "Purchase" button which calls a `purchase` function that
spawns a network request and sends the `cart` array to the server. Because
of a bad network connection, the `purchase` function has to keep retrying the
request. Now, what if in the meantime the user accidentally clicks an "Add to Cart"
button on an item they don't actually want before the network request begins?
If that happens and the network request begins, then that purchase function
will send the accidentally added item because the `cart` array was modified.

A great solution would be for the `addItemToCart` function to always clone the 
`cart`, edit it, and return the clone. This would ensure that functions that are still
using the old shopping cart wouldn't be affected by the changes.

Two caveats to mention to this approach:

1. There might be cases where you actually want to modify the input object,
   but when you adopt this programming practice you will find that those cases
   are pretty rare. Most things can be refactored to have no side effects!

2. Cloning big objects can be very expensive in terms of performance. Luckily,
   this isn't a big issue in practice because there are
   [great libraries](https://facebook.github.io/immutable-js/) that allow
   this kind of programming approach to be fast and not as memory intensive as
   it would be for you to manually clone objects and arrays.

**Bad:**

```javascript
const addItemToCart = (cart, item) => {
  cart.push({ item, date: Date.now() });
};
```

**Good:**

```javascript
const addItemToCart = (cart, item) => {
  return [...cart, { item, date: Date.now() }];
};
```

**[⬆ back to top](#table-of-contents)**

### Don't write to global functions

Polluting globals is a bad practice in JavaScript because you could clash with another
library and the user of your API would be none-the-wiser until they get an
exception in production. Let's think about an example: what if you wanted to
extend JavaScript's native Array method to have a `diff` method that could
show the difference between two arrays? You could write your new function
to the `Array.prototype`, but it could clash with another library that tried
to do the same thing. What if that other library was just using `diff` to find
the difference between the first and last elements of an array? This is why it
would be much better to just use ES2015/ES6 classes and simply extend the `Array` global.

**Bad:**

```javascript
Array.prototype.diff = function diff(comparisonArray) {
  const hash = new Set(comparisonArray);
  return this.filter(elem => !hash.has(elem));
};
```

**Good:**

```javascript
class SuperArray extends Array {
  diff(comparisonArray) {
    const hash = new Set(comparisonArray);
    return this.filter(elem => !hash.has(elem));
  }
}
```

**[⬆ back to top](#table-of-contents)**

### Favor functional programming over imperative programming

JavaScript isn't a functional language in the way that Haskell is, but it has
a functional flavor to it. Functional languages can be cleaner and easier to test.
Favor this style of programming when you can.

**Bad:**

```javascript
const programmerOutput = [
  {
    name: "Uncle Bobby",
    linesOfCode: 500
  },
  {
    name: "Suzie Q",
    linesOfCode: 1500
  },
  {
    name: "Jimmy Gosling",
    linesOfCode: 150
  },
  {
    name: "Gracie Hopper",
    linesOfCode: 1000
  }
];

let totalOutput = 0;

for (let i = 0; i < programmerOutput.length; i++) {
  totalOutput += programmerOutput[i].linesOfCode;
}
```

**Good:**

```javascript
const programmerOutput = [
  {
    name: "Uncle Bobby",
    linesOfCode: 500
  },
  {
    name: "Suzie Q",
    linesOfCode: 1500
  },
  {
    name: "Jimmy Gosling",
    linesOfCode: 150
  },
  {
    name: "Gracie Hopper",
    linesOfCode: 1000
  }
];

const totalOutput = programmerOutput.reduce(
  (totalLines, output) => totalLines + output.linesOfCode,
  0
);
```

**[⬆ back to top](#table-of-contents)**

### Encapsulate conditionals

**Bad:**

```javascript
if (fsm.state === "fetching" && isEmpty(listNode)) {
  // ...
}
```

**Good:**

```javascript
function shouldShowSpinner(fsm, listNode) {
  return fsm.state === "fetching" && isEmpty(listNode);
}

if (shouldShowSpinner(fsmInstance, listNodeInstance)) {
  // ...
}
```

**[⬆ back to top](#table-of-contents)**

### Avoid negative conditionals

**Bad:**

```javascript
function isDOMNodeNotPresent(node) {
  // ...
}

if (!isDOMNodeNotPresent(node)) {
  // ...
}
```

**Good:**

```javascript
function isDOMNodePresent(node) {
  // ...
}

if (isDOMNodePresent(node)) {
  // ...
}
```

**[⬆ back to top](#table-of-contents)**

### Avoid conditionals

This seems like an impossible task. Upon first hearing this, most people say,
"how am I supposed to do anything without an `if` statement?" The answer is that
you can use polymorphism to achieve the same task in many cases. The second
question is usually, "well that's great but why would I want to do that?" The
answer is a previous clean code concept we learned: a function should only do
one thing. When you have classes and functions that have `if` statements, you
are telling your user that your function does more than one thing. Remember,
just do one thing.

**Bad:**

```javascript
class Airplane {
  // ...
  getCruisingAltitude() {
    switch (this.type) {
      case "777":
        return this.getMaxAltitude() - this.getPassengerCount();
      case "Air Force One":
        return this.getMaxAltitude();
      case "Cessna":
        return this.getMaxAltitude() - this.getFuelExpenditure();
    }
  }
}
```

**Good:**

```javascript
class Airplane {
  // ...
}

class Boeing777 extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude() - this.getPassengerCount();
  }
}

class AirForceOne extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude();
  }
}

class Cessna extends Airplane {
  // ...
  getCruisingAltitude() {
    return this.getMaxAltitude() - this.getFuelExpenditure();
  }
}
```

**[⬆ back to top](#table-of-contents)**

### Avoid type-checking (part 1)

JavaScript is untyped, which means your functions can take any type of argument.
Sometimes you are bitten by this freedom and it becomes tempting to do
type-checking in your functions. There are many ways to avoid having to do this.
The first thing to consider is consistent APIs.

**Bad:**

```javascript
function travelToTexas(vehicle) {
  if (vehicle instanceof Bicycle) {
    vehicle.pedal(this.currentLocation, new Location("texas"));
  } else if (vehicle instanceof Car) {
    vehicle.drive(this.currentLocation, new Location("texas"));
  }
}
```

**Good:**

```javascript
function travelToTexas(vehicle) {
  vehicle.move(this.currentLocation, new Location("texas"));
}
```

**[⬆ back to top](#table-of-contents)**

### Avoid type-checking (part 2)

If you are working with basic primitive values like strings and integers,
and you can't use polymorphism but you still feel the need to type-check,
you should consider using TypeScript. It is an excellent alternative to normal
JavaScript, as it provides you with static typing on top of standard JavaScript
syntax. The problem with manually type-checking normal JavaScript is that
doing it well requires so much extra verbiage that the faux "type-safety" you get
doesn't make up for the lost readability. Keep your JavaScript clean, write
good tests, and have good code reviews. Otherwise, do all of that but with
TypeScript (which, like I said, is a great alternative!).

**Bad:**

```javascript
function combine(val1, val2) {
  if (
    (typeof val1 === "number" && typeof val2 === "number") ||
    (typeof val1 === "string" && typeof val2 === "string")
  ) {
    return val1 + val2;
  }

  throw new Error("Must be of type String or Number");
}
```

**Good:**

```javascript
function combine(val1, val2) {
  return val1 + val2;
}
```

**[⬆ back to top](#table-of-contents)**

### Don't over-optimize

Modern browsers do a lot of optimization under-the-hood at runtime. A lot of
times, if you are optimizing then you are just wasting your time. [There are good
resources](https://github.com/petkaantonov/bluebird/wiki/Optimization-killers)
for seeing where optimization is lacking. Target those in the meantime, until
they are fixed if they can be.

**Bad:**

```javascript
// On old browsers, each iteration with uncached `list.length` would be costly
// because of `list.length` recomputation. In modern browsers, this is optimized.
for (let i = 0, len = list.length; i < len; i++) {
  // ...
}
```

**Good:**

```javascript
for (let i = 0; i < list.length; i++) {
  // ...
}
```

**[⬆ back to top](#table-of-contents)**

### Remove dead code

Dead code is just as bad as duplicate code. There's no reason to keep it in
your codebase. If it's not being called, get rid of it! It will still be safe
in your version history if you still need it.

**Bad:**

```javascript
function oldRequestModule(url) {
  // ...
}

function newRequestModule(url) {
  // ...
}

const req = newRequestModule;
inventoryTracker("apples", req, "www.inventory-awesome.io");
```

**Good:**

```javascript
function newRequestModule(url) {
  // ...
}

const req = newRequestModule;
inventoryTracker("apples", req, "www.inventory-awesome.io");
```

**[⬆ back to top](#table-of-contents)**

## **Objects and Data Structures**

### Use getters and setters

Using getters and setters to access data on objects could be better than simply
looking for a property on an object. "Why?" you might ask. Well, here's an
unorganized list of reasons why:

- When you want to do more beyond getting an object property, you don't have
  to look up and change every accessor in your codebase.
- Makes adding validation simple when doing a `set`.
- Encapsulates the internal representation.
- Easy to add logging and error handling when getting and setting.
- You can lazy load your object's properties, let's say getting it from a
  server.

**Bad:**

```javascript
function makeBankAccount() {
  // ...

  return {
    balance: 0
    // ...
  };
}

const account = makeBankAccount();
account.balance = 100;
```

**Good:**

```javascript
function makeBankAccount() {
  // this one is private
  let balance = 0;

  // a "getter", made public via the returned object below
  function getBalance() {
    return balance;
  }

  // a "setter", made public via the returned object below
  function setBalance(amount) {
    // ... validate before updating the balance
    balance = amount;
  }

  return {
    // ...
    getBalance,
    setBalance
  };
}

const account = makeBankAccount();
account.setBalance(100);
```

**[⬆ back to top](#table-of-contents)**

### Make objects have private members

This can be accomplished through closures (for ES5 and below).

**Bad:**

```javascript
const Employee = function(name) {
  this.name = name;
};

Employee.prototype.getName = function getName() {
  return this.name;
};

const employee = new Employee("John Doe");
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: undefined
```

**Good:**

```javascript
function makeEmployee(name) {
  return {
    getName() {
      return name;
    }
  };
}

const employee = makeEmployee("John Doe");
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
```

**[⬆ back to top](#table-of-contents)**

## **Classes**

### Prefer ES2015/ES6 classes over ES5 plain functions

It's very difficult to get readable class inheritance, construction, and method
definitions for classical ES5 classes. If you need inheritance (and be aware
that you might not), then prefer ES2015/ES6 classes. However, prefer small functions over
classes until you find yourself needing larger and more complex objects.

**Bad:**

```javascript
const Animal = function(age) {
  if (!(this instanceof Animal)) {
    throw new Error("Instantiate Animal with `new`");
  }

  this.age = age;
};

Animal.prototype.move = function move() {};

const Mammal = function(age, furColor) {
  if (!(this instanceof Mammal)) {
    throw new Error("Instantiate Mammal with `new`");
  }

  Animal.call(this, age);
  this.furColor = furColor;
};

Mammal.prototype = Object.create(Animal.prototype);
Mammal.prototype.constructor = Mammal;
Mammal.prototype.liveBirth = function liveBirth() {};

const Human = function(age, furColor, languageSpoken) {
  if (!(this instanceof Human)) {
    throw new Error("Instantiate Human with `new`");
  }

  Mammal.call(this, age, furColor);
  this.languageSpoken = languageSpoken;
};

Human.prototype = Object.create(Mammal.prototype);
Human.prototype.constructor = Human;
Human.prototype.speak = function speak() {};
```

**Good:**

```javascript
class Animal {
  constructor(age) {
    this.age = age;
  }

  move() {
    /* ... */
  }
}

class Mammal extends Animal {
  constructor(age, furColor) {
    super(age);
    this.furColor = furColor;
  }

  liveBirth() {
    /* ... */
  }
}

class Human extends Mammal {
  constructor(age, furColor, languageSpoken) {
    super(age, furColor);
    this.languageSpoken = languageSpoken;
  }

  speak() {
    /* ... */
  }
}
```

**[⬆ back to top](#table-of-contents)**

### Use method chaining

This pattern is very useful in JavaScript and you see it in many libraries such
as jQuery and Lodash. It allows your code to be expressive, and less verbose.
For that reason, I say, use method chaining and take a look at how clean your code
will be. In your class functions, simply return `this` at the end of every function,
and you can chain further class methods onto it.

**Bad:**

```javascript
class Car {
  constructor(make, model, color) {
    this.make = make;
    this.model = model;
    this.color = color;
  }

  setMake(make) {
    this.make = make;
  }

  setModel(model) {
    this.model = model;
  }

  setColor(color) {
    this.color = color;
  }

  save() {
    console.log(this.make, this.model, this.color);
  }
}

const car = new Car("Ford", "F-150", "red");
car.setColor("pink");
car.save();
```

**Good:**

```javascript
class Car {
  constructor(make, model, color) {
    this.make = make;
    this.model = model;
    this.color = color;
  }

  setMake(make) {
    this.make = make;
    // NOTE: Returning this for chaining
    return this;
  }

  setModel(model) {
    this.model = model;
    // NOTE: Returning this for chaining
    return this;
  }

  setColor(color) {
    this.color = color;
    // NOTE: Returning this for chaining
    return this;
  }

  save() {
    console.log(this.make, this.model, this.color);
    // NOTE: Returning this for chaining
    return this;
  }
}

const car = new Car("Ford", "F-150", "red").setColor("pink").save();
```

**[⬆ back to top](#table-of-contents)**

### Prefer composition over inheritance

As stated famously in [_Design Patterns_](https://en.wikipedia.org/wiki/Design_Patterns) by the Gang of Four,
you should prefer composition over inheritance where you can. There are lots of
good reasons to use inheritance and lots of good reasons to use composition.
The main point for this maxim is that if your mind instinctively goes for
inheritance, try to think if composition could model your problem better. In some
cases it can.

You might be wondering then, "when should I use inheritance?" It
depends on your problem at hand, but this is a decent list of when inheritance
makes more sense than composition:

1. Your inheritance represents an "is-a" relationship and not a "has-a"
   relationship (Human->Animal vs. User->UserDetails).
2. You can reuse code from the base classes (Humans can move like all animals).
3. You want to make global changes to derived classes by changing a base class.
   (Change the caloric expenditure of all animals when they move).

**Bad:**

```javascript
class Employee {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }

  // ...
}

// Bad because Employees "have" tax data. EmployeeTaxData is not a type of Employee
class EmployeeTaxData extends Employee {
  constructor(ssn, salary) {
    super();
    this.ssn = ssn;
    this.salary = salary;
  }

  // ...
}
```

**Good:**

```javascript
class EmployeeTaxData {
  constructor(ssn, salary) {
    this.ssn = ssn;
    this.salary = salary;
  }

  // ...
}

class Employee {
  constructor(name, email) {
    this.name = name;
    this.email = email;
  }

  setTaxData(ssn, salary) {
    this.taxData = new EmployeeTaxData(ssn, salary);
  }
  // ...
}
```

**[⬆ back to top](#table-of-contents)**

## **SOLID**

### Single Responsibility Principle (SRP)

As stated in Clean Code, "There should never be more than one reason for a class
to change". It's tempting to jam-pack a class with a lot of functionality, like
when you can only take one suitcase on your flight. The issue with this is
that your class won't be conceptually cohesive and it will give it many reasons
to change. Minimizing the amount of times you need to change a class is important.
It's important because if too much functionality is in one class and you modify
a piece of it, it can be difficult to understand how that will affect other
dependent modules in your codebase.

**Bad:**

```javascript
class UserSettings {
  constructor(user) {
    this.user = user;
  }

  changeSettings(settings) {
    if (this.verifyCredentials()) {
      // ...
    }
  }

  verifyCredentials() {
    // ...
  }
}
```

**Good:**

```javascript
class UserAuth {
  constructor(user) {
    this.user = user;
  }

  verifyCredentials() {
    // ...
  }
}

class UserSettings {
  constructor(user) {
    this.user = user;
    this.auth = new UserAuth(user);
  }

  changeSettings(settings) {
    if (this.auth.verifyCredentials()) {
      // ...
    }
  }
}
```

**[⬆ back to top](#table-of-contents)**

### Open/Closed Principle (OCP)

As stated by Bertrand Meyer, "software entities (classes, modules, functions,
etc.) should be open for extension, but closed for modification." What does that
mean though? This principle basically states that you should allow users to
add new functionalities without changing existing code.

**Bad:**

```javascript
class AjaxAdapter extends Adapter {
  constructor() {
    super();
    this.name = "ajaxAdapter";
  }
}

class NodeAdapter extends Adapter {
  constructor() {
    super();
    this.name = "nodeAdapter";
  }
}

class HttpRequester {
  constructor(adapter) {
    this.adapter = adapter;
  }

  fetch(url) {
    if (this.adapter.name === "ajaxAdapter") {
      return makeAjaxCall(url).then(response => {
        // transform response and return
      });
    } else if (this.adapter.name === "nodeAdapter") {
      return makeHttpCall(url).then(response => {
        // transform response and return
      });
    }
  }
}

function makeAjaxCall(url) {
  // request and return promise
}

function makeHttpCall(url) {
  // request and return promise
}
```

**Good:**

```javascript
class AjaxAdapter extends Adapter {
  constructor() {
    super();
    this.name = "ajaxAdapter";
  }

  request(url) {
    // request and return promise
  }
}

class NodeAdapter extends Adapter {
  constructor() {
    super();
    this.name = "nodeAdapter";
  }

  request(url) {
    // request and return promise
  }
}

class HttpRequester {
  constructor(adapter) {
    this.adapter = adapter;
  }

  fetch(url) {
    return this.adapter.request(url).then(response => {
      // transform response and return
    });
  }
}
```

**[⬆ back to top](#table-of-contents)**

### Liskov Substitution Principle (LSP)

This is a scary term for a very simple concept. It's formally defined as "If S
is a subtype of T, then objects of type T may be replaced with objects of type S
(i.e., objects of type S may substitute objects of type T) without altering any
of the desirable properties of that program (correctness, task performed,
etc.)." That's an even scarier definition.

The best explanation for this is if you have a parent class and a child class,
then the base class and child class can be used interchangeably without getting
incorrect results. This might still be confusing, so let's take a look at the
classic Square-Rectangle example. Mathematically, a square is a rectangle, but
if you model it using the "is-a" relationship via inheritance, you quickly
get into trouble.

**Bad:**

```javascript
class Rectangle {
  constructor() {
    this.width = 0;
    this.height = 0;
  }

  setColor(color) {
    // ...
  }

  render(area) {
    // ...
  }

  setWidth(width) {
    this.width = width;
  }

  setHeight(height) {
    this.height = height;
  }

  getArea() {
    return this.width * this.height;
  }
}

class Square extends Rectangle {
  setWidth(width) {
    this.width = width;
    this.height = width;
  }

  setHeight(height) {
    this.width = height;
    this.height = height;
  }
}

function renderLargeRectangles(rectangles) {
  rectangles.forEach(rectangle => {
    rectangle.setWidth(4);
    rectangle.setHeight(5);
    const area = rectangle.getArea(); // BAD: Returns 25 for Square. Should be 20.
    rectangle.render(area);
  });
}

const rectangles = [new Rectangle(), new Rectangle(), new Square()];
renderLargeRectangles(rectangles);
```

**Good:**

```javascript
class Shape {
  setColor(color) {
    // ...
  }

  render(area) {
    // ...
  }
}

class Rectangle extends Shape {
  constructor(width, height) {
    super();
    this.width = width;
    this.height = height;
  }

  getArea() {
    return this.width * this.height;
  }
}

class Square extends Shape {
  constructor(length) {
    super();
    this.length = length;
  }

  getArea() {
    return this.length * this.length;
  }
}

function renderLargeShapes(shapes) {
  shapes.forEach(shape => {
    const area = shape.getArea();
    shape.render(area);
  });
}

const shapes = [new Rectangle(4, 5), new Rectangle(4, 5), new Square(5)];
renderLargeShapes(shapes);
```

**[⬆ back to top](#table-of-contents)**

### Interface Segregation Principle (ISP)

JavaScript doesn't have interfaces so this principle doesn't apply as strictly
as others. However, it's important and relevant even with JavaScript's lack of
type system.

ISP states that "Clients should not be forced to depend upon interfaces that
they do not use." Interfaces are implicit contracts in JavaScript because of
duck typing.

A good example to look at that demonstrates this principle in JavaScript is for
classes that require large settings objects. Not requiring clients to setup
huge amounts of options is beneficial, because most of the time they won't need
all of the settings. Making them optional helps prevent having a
"fat interface".

**Bad:**

```javascript
class DOMTraverser {
  constructor(settings) {
    this.settings = settings;
    this.setup();
  }

  setup() {
    this.rootNode = this.settings.rootNode;
    this.settings.animationModule.setup();
  }

  traverse() {
    // ...
  }
}

const $ = new DOMTraverser({
  rootNode: document.getElementsByTagName("body"),
  animationModule() {} // Most of the time, we won't need to animate when traversing.
  // ...
});
```

**Good:**

```javascript
class DOMTraverser {
  constructor(settings) {
    this.settings = settings;
    this.options = settings.options;
    this.setup();
  }

  setup() {
    this.rootNode = this.settings.rootNode;
    this.setupOptions();
  }

  setupOptions() {
    if (this.options.animationModule) {
      // ...
    }
  }

  traverse() {
    // ...
  }
}

const $ = new DOMTraverser({
  rootNode: document.getElementsByTagName("body"),
  options: {
    animationModule() {}
  }
});
```

**[⬆ back to top](#table-of-contents)**

### Dependency Inversion Principle (DIP)

This principle states two essential things:

1. High-level modules should not depend on low-level modules. Both should
   depend on abstractions.
2. Abstractions should not depend upon details. Details should depend on
   abstractions.

This can be hard to understand at first, but if you've worked with AngularJS,
you've seen an implementation of this principle in the form of Dependency
Injection (DI). While they are not identical concepts, DIP keeps high-level
modules from knowing the details of its low-level modules and setting them up.
It can accomplish this through DI. A huge benefit of this is that it reduces
the coupling between modules. Coupling is a very bad development pattern because
it makes your code hard to refactor.

As stated previously, JavaScript doesn't have interfaces so the abstractions
that are depended upon are implicit contracts. That is to say, the methods
and properties that an object/class exposes to another object/class. In the
example below, the implicit contract is that any Request module for an
`InventoryTracker` will have a `requestItems` method.

**Bad:**

```javascript
class InventoryRequester {
  constructor() {
    this.REQ_METHODS = ["HTTP"];
  }

  requestItem(item) {
    // ...
  }
}

class InventoryTracker {
  constructor(items) {
    this.items = items;

    // BAD: We have created a dependency on a specific request implementation.
    // We should just have requestItems depend on a request method: `request`
    this.requester = new InventoryRequester();
  }

  requestItems() {
    this.items.forEach(item => {
      this.requester.requestItem(item);
    });
  }
}

const inventoryTracker = new InventoryTracker(["apples", "bananas"]);
inventoryTracker.requestItems();
```

**Good:**

```javascript
class InventoryTracker {
  constructor(items, requester) {
    this.items = items;
    this.requester = requester;
  }

  requestItems() {
    this.items.forEach(item => {
      this.requester.requestItem(item);
    });
  }
}

class InventoryRequesterV1 {
  constructor() {
    this.REQ_METHODS = ["HTTP"];
  }

  requestItem(item) {
    // ...
  }
}

class InventoryRequesterV2 {
  constructor() {
    this.REQ_METHODS = ["WS"];
  }

  requestItem(item) {
    // ...
  }
}

// By constructing our dependencies externally and injecting them, we can easily
// substitute our request module for a fancy new one that uses WebSockets.
const inventoryTracker = new InventoryTracker(
  ["apples", "bananas"],
  new InventoryRequesterV2()
);
inventoryTracker.requestItems();
```

**[⬆ back to top](#table-of-contents)**

## **Testing**

Testing is more important than shipping. If you have no tests or an
inadequate amount, then every time you ship code you won't be sure that you
didn't break anything. Deciding on what constitutes an adequate amount is up
to your team, but having 100% coverage (all statements and branches) is how
you achieve very high confidence and developer peace of mind. This means that
in addition to having a great testing framework, you also need to use a
[good coverage tool](https://gotwarlost.github.io/istanbul/).

There's no excuse to not write tests. There are [plenty of good JS test frameworks](https://jstherightway.org/#testing-tools), so find one that your team prefers.
When you find one that works for your team, then aim to always write tests
for every new feature/module you introduce. If your preferred method is
Test Driven Development (TDD), that is great, but the main point is to just
make sure you are reaching your coverage goals before launching any feature,
or refactoring an existing one.

### Single concept per test

**Bad:**

```javascript
import assert from "assert";

describe("MomentJS", () => {
  it("handles date boundaries", () => {
    let date;

    date = new MomentJS("1/1/2015");
    date.addDays(30);
    assert.equal("1/31/2015", date);

    date = new MomentJS("2/1/2016");
    date.addDays(28);
    assert.equal("02/29/2016", date);

    date = new MomentJS("2/1/2015");
    date.addDays(28);
    assert.equal("03/01/2015", date);
  });
});
```

**Good:**

```javascript
import assert from "assert";

describe("MomentJS", () => {
  it("handles 30-day months", () => {
    const date = new MomentJS("1/1/2015");
    date.addDays(30);
    assert.equal("1/31/2015", date);
  });

  it("handles leap year", () => {
    const date = new MomentJS("2/1/2016");
    date.addDays(28);
    assert.equal("02/29/2016", date);
  });

  it("handles non-leap year", () => {
    const date = new MomentJS("2/1/2015");
    date.addDays(28);
    assert.equal("03/01/2015", date);
  });
});
```

**[⬆ back to top](#table-of-contents)**

## **Concurrency**

### Use Promises, not callbacks

Callbacks aren't clean, and they cause excessive amounts of nesting. With ES2015/ES6,
Promises are a built-in global type. Use them!

**Bad:**

```javascript
import { get } from "request";
import { writeFile } from "fs";

get(
  "https://en.wikipedia.org/wiki/Robert_Cecil_Martin",
  (requestErr, response, body) => {
    if (requestErr) {
      console.error(requestErr);
    } else {
      writeFile("article.html", body, writeErr => {
        if (writeErr) {
          console.error(writeErr);
        } else {
          console.log("File written");
        }
      });
    }
  }
);
```

**Good:**

```javascript
import { get } from "request-promise";
import { writeFile } from "fs-extra";

get("https://en.wikipedia.org/wiki/Robert_Cecil_Martin")
  .then(body => {
    return writeFile("article.html", body);
  })
  .then(() => {
    console.log("File written");
  })
  .catch(err => {
    console.error(err);
  });
```

**[⬆ back to top](#table-of-contents)**

### Async/Await are even cleaner than Promises

Promises are a very clean alternative to callbacks, but ES2017/ES8 brings async and await
which offer an even cleaner solution. All you need is a function that is prefixed
in an `async` keyword, and then you can write your logic imperatively without
a `then` chain of functions. Use this if you can take advantage of ES2017/ES8 features
today!

**Bad:**

```javascript
import { get } from "request-promise";
import { writeFile } from "fs-extra";

get("https://en.wikipedia.org/wiki/Robert_Cecil_Martin")
  .then(body => {
    return writeFile("article.html", body);
  })
  .then(() => {
    console.log("File written");
  })
  .catch(err => {
    console.error(err);
  });
```

**Good:**

```javascript
import { get } from "request-promise";
import { writeFile } from "fs-extra";

async function getCleanCodeArticle() {
  try {
    const body = await get(
      "https://en.wikipedia.org/wiki/Robert_Cecil_Martin"
    );
    await writeFile("article.html", body);
    console.log("File written");
  } catch (err) {
    console.error(err);
  }
}

getCleanCodeArticle()
```

**[⬆ back to top](#table-of-contents)**

## **Error Handling**

Thrown errors are a good thing! They mean the runtime has successfully
identified when something in your program has gone wrong and it's letting
you know by stopping function execution on the current stack, killing the
process (in Node), and notifying you in the console with a stack trace.

### Don't ignore caught errors

Doing nothing with a caught error doesn't give you the ability to ever fix
or react to said error. Logging the error to the console (`console.log`)
isn't much better as often times it can get lost in a sea of things printed
to the console. If you wrap any bit of code in a `try/catch` it means you
think an error may occur there and therefore you should have a plan,
or create a code path, for when it occurs.

**Bad:**

```javascript
try {
  functionThatMightThrow();
} catch (error) {
  console.log(error);
}
```

**Good:**

```javascript
try {
  functionThatMightThrow();
} catch (error) {
  // One option (more noisy than console.log):
  console.error(error);
  // Another option:
  notifyUserOfError(error);
  // Another option:
  reportErrorToService(error);
  // OR do all three!
}
```

### Don't ignore rejected promises

For the same reason you shouldn't ignore caught errors
from `try/catch`.

**Bad:**

```javascript
getdata()
  .then(data => {
    functionThatMightThrow(data);
  })
  .catch(error => {
    console.log(error);
  });
```

**Good:**

```javascript
getdata()
  .then(data => {
    functionThatMightThrow(data);
  })
  .catch(error => {
    // One option (more noisy than console.log):
    console.error(error);
    // Another option:
    notifyUserOfError(error);
    // Another option:
    reportErrorToService(error);
    // OR do all three!
  });
```

**[⬆ back to top](#table-of-contents)**

## **Formatting**

Formatting is subjective. Like many rules herein, there is no hard and fast
rule that you must follow. The main point is DO NOT ARGUE over formatting.
There are [tons of tools](https://standardjs.com/rules.html) to automate this.
Use one! It's a waste of time and money for engineers to argue over formatting.

For things that don't fall under the purview of automatic formatting
(indentation, tabs vs. spaces, double vs. single quotes, etc.) look here
for some guidance.

### Use consistent capitalization

JavaScript is untyped, so capitalization tells you a lot about your variables,
functions, etc. These rules are subjective, so your team can choose whatever
they want. The point is, no matter what you all choose, just be consistent.

**Bad:**

```javascript
const DAYS_IN_WEEK = 7;
const daysInMonth = 30;

const songs = ["Back In Black", "Stairway to Heaven", "Hey Jude"];
const Artists = ["ACDC", "Led Zeppelin", "The Beatles"];

function eraseDatabase() {}
function restore_database() {}

class animal {}
class Alpaca {}
```

**Good:**

```javascript
const DAYS_IN_WEEK = 7;
const DAYS_IN_MONTH = 30;

const SONGS = ["Back In Black", "Stairway to Heaven", "Hey Jude"];
const ARTISTS = ["ACDC", "Led Zeppelin", "The Beatles"];

function eraseDatabase() {}
function restoreDatabase() {}

class Animal {}
class Alpaca {}
```

**[⬆ back to top](#table-of-contents)**

### Function callers and callees should be close

If a function calls another, keep those functions vertically close in the source
file. Ideally, keep the caller right above the callee. We tend to read code from
top-to-bottom, like a newspaper. Because of this, make your code read that way.

**Bad:**

```javascript
class PerformanceReview {
  constructor(employee) {
    this.employee = employee;
  }

  lookupPeers() {
    return db.lookup(this.employee, "peers");
  }

  lookupManager() {
    return db.lookup(this.employee, "manager");
  }

  getPeerReviews() {
    const peers = this.lookupPeers();
    // ...
  }

  perfReview() {
    this.getPeerReviews();
    this.getManagerReview();
    this.getSelfReview();
  }

  getManagerReview() {
    const manager = this.lookupManager();
  }

  getSelfReview() {
    // ...
  }
}

const review = new PerformanceReview(employee);
review.perfReview();
```

**Good:**

```javascript
class PerformanceReview {
  constructor(employee) {
    this.employee = employee;
  }

  perfReview() {
    this.getPeerReviews();
    this.getManagerReview();
    this.getSelfReview();
  }

  getPeerReviews() {
    const peers = this.lookupPeers();
    // ...
  }

  lookupPeers() {
    return db.lookup(this.employee, "peers");
  }

  getManagerReview() {
    const manager = this.lookupManager();
  }

  lookupManager() {
    return db.lookup(this.employee, "manager");
  }

  getSelfReview() {
    // ...
  }
}

const review = new PerformanceReview(employee);
review.perfReview();
```

**[⬆ back to top](#table-of-contents)**

## **Comments**

### Only comment things that have business logic complexity.

Comments are an apology, not a requirement. Good code _mostly_ documents itself.

**Bad:**

```javascript
function hashIt(data) {
  // The hash
  let hash = 0;

  // Length of string
  const length = data.length;

  // Loop through every character in data
  for (let i = 0; i < length; i++) {
    // Get character code.
    const char = data.charCodeAt(i);
    // Make the hash
    hash = (hash << 5) - hash + char;
    // Convert to 32-bit integer
    hash &= hash;
  }
}
```

**Good:**

```javascript
function hashIt(data) {
  let hash = 0;
  const length = data.length;

  for (let i = 0; i < length; i++) {
    const char = data.charCodeAt(i);
    hash = (hash << 5) - hash + char;

    // Convert to 32-bit integer
    hash &= hash;
  }
}
```

**[⬆ back to top](#table-of-contents)**

### Don't leave commented out code in your codebase

Version control exists for a reason. Leave old code in your history.

**Bad:**

```javascript
doStuff();
// doOtherStuff();
// doSomeMoreStuff();
// doSoMuchStuff();
```

**Good:**

```javascript
doStuff();
```

**[⬆ back to top](#table-of-contents)**

### Don't have journal comments

Remember, use version control! There's no need for dead code, commented code,
and especially journal comments. Use `git log` to get history!

**Bad:**

```javascript
/**
 * 2016-12-20: Removed monads, didn't understand them (RM)
 * 2016-10-01: Improved using special monads (JP)
 * 2016-02-03: Removed type-checking (LI)
 * 2015-03-14: Added combine with type-checking (JR)
 */
function combine(a, b) {
  return a + b;
}
```

**Good:**

```javascript
function combine(a, b) {
  return a + b;
}
```

**[⬆ back to top](#table-of-contents)**

### Avoid positional markers

They usually just add noise. Let the functions and variable names along with the
proper indentation and formatting give the visual structure to your code.

**Bad:**

```javascript
////////////////////////////////////////////////////////////////////////////////
// Scope Model Instantiation
////////////////////////////////////////////////////////////////////////////////
$scope.model = {
  menu: "foo",
  nav: "bar"
};

////////////////////////////////////////////////////////////////////////////////
// Action setup
////////////////////////////////////////////////////////////////////////////////
const actions = function() {
  // ...
};
```

**Good:**

```javascript
$scope.model = {
  menu: "foo",
  nav: "bar"
};

const actions = function() {
  // ...
};
```

**[⬆ back to top](#table-of-contents)**

## Translation

This is also available in other languages:

- ![am](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Armenia.png) **Armenian**: [hanumanum/clean-code-javascript/](https://github.com/hanumanum/clean-code-javascript)
- ![bd](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Bangladesh.png) **Bangla(বাংলা)**: [InsomniacSabbir/clean-code-javascript/](https://github.com/InsomniacSabbir/clean-code-javascript/)
- ![br](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Brazil.png) **Brazilian Portuguese**: [fesnt/clean-code-javascript](https://github.com/fesnt/clean-code-javascript)
- ![cn](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/China.png) **Simplified Chinese**:
  - [alivebao/clean-code-js](https://github.com/alivebao/clean-code-js)
  - [beginor/clean-code-javascript](https://github.com/beginor/clean-code-javascript)
- ![tw](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Taiwan.png) **Traditional Chinese**: [AllJointTW/clean-code-javascript](https://github.com/AllJointTW/clean-code-javascript)
- ![fr](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/France.png) **French**: [GavBaros/clean-code-javascript-fr](https://github.com/GavBaros/clean-code-javascript-fr)
- ![de](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Germany.png) **German**: [marcbruederlin/clean-code-javascript](https://github.com/marcbruederlin/clean-code-javascript)
- ![id](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Indonesia.png) **Indonesia**: [andirkh/clean-code-javascript/](https://github.com/andirkh/clean-code-javascript/)
- ![it](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Italy.png) **Italian**: [frappacchio/clean-code-javascript/](https://github.com/frappacchio/clean-code-javascript/)
- ![ja](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Japan.png) **Japanese**: [mitsuruog/clean-code-javascript/](https://github.com/mitsuruog/clean-code-javascript/)
- ![kr](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/South-Korea.png) **Korean**: [qkraudghgh/clean-code-javascript-ko](https://github.com/qkraudghgh/clean-code-javascript-ko)
- ![pl](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Poland.png) **Polish**: [greg-dev/clean-code-javascript-pl](https://github.com/greg-dev/clean-code-javascript-pl)
- ![ru](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Russia.png) **Russian**:
  - [BoryaMogila/clean-code-javascript-ru/](https://github.com/BoryaMogila/clean-code-javascript-ru/)
  - [maksugr/clean-code-javascript](https://github.com/maksugr/clean-code-javascript)
- ![es](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Spain.png) **Spanish**: [tureey/clean-code-javascript](https://github.com/tureey/clean-code-javascript)
- ![es](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Uruguay.png) **Spanish**: [andersontr15/clean-code-javascript](https://github.com/andersontr15/clean-code-javascript-es)
- ![rs](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Serbia.png) **Serbian**: [doskovicmilos/clean-code-javascript/](https://github.com/doskovicmilos/clean-code-javascript)
- ![tr](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Turkey.png) **Turkish**: [bsonmez/clean-code-javascript](https://github.com/bsonmez/clean-code-javascript/tree/turkish-translation)
- ![ua](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Ukraine.png) **Ukrainian**: [mindfr1k/clean-code-javascript-ua](https://github.com/mindfr1k/clean-code-javascript-ua)
- ![vi](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Vietnam.png) **Vietnamese**: [hienvd/clean-code-javascript/](https://github.com/hienvd/clean-code-javascript/)

**[⬆ back to top](#table-of-contents)**