JavaScript style guide

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There’s more than one way to do it, but sometimes consistency is not a bad thing either. (TIMTOWTDIBSCINABTE)
Now is better than never.
Although later is often better than right now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.

_{* Borrowed from Python zen with slight modifications. [+]}

Naming conventions

Folders and files

kebab-case for folders.

Covers if folder will be extracted to its own package some day. [+]

camelCase or PascalCase for files.

Has problems on commiting case-sensitive filename changes with Git. [+]

✔️ Good

.
└── src/
    ├── product/
    │   ├── application/
    │   │   └── services/
    │   │       └── SearchProductsService.js
    │   ├── domain/
    │   │   └── services/
    │   │       └── SearchProductsBySKUService.js
    │   └── infrastructure/
    │       └── stores/
    │           └── ProductAPIStore.js
    └── app.js

_{* Generated with https://tree.nathanfriend.io/.}

A file that exports only one class, function, or constant should be named for that class, function or constant.

❌ Bad

// file name: programstore.js

export class ProgramStore {
  ...
}

✔️ Good

// file name: ProgramStore.js

export class ProgramStore {
  ...
}

Files whose exports multiple things, the file name should be kept short, meaningful and easily understandable to others.

Avoid index as a file name.

It does not reflect the content of the file.

The file can’t live outside of the folder, because breaks the chain between folder name and file name.

NodeJS has a special treatment for index files, but other engines like Deno don’t.

❌ Bad

.
└── src/
    └── program-filters/
        ├── isNotOldFilter.js
        ├── hasMonthlyDownloadsFilter.js
        └── index.js

✔️ Good

.
└── src/
    └── program-filters/
        ├── isNotOldFilter.js
        ├── hasMonthlyDownloadsFilter.js
        └── programFilters.js

Avoid generic names for folders. Be precise.

❌ Bad

.
└── src/
    ├── utils/
    ├── config/
    ├── vendors/
    └── helpers/

✔️ Good

.
└── src/
    ├── program-guards/
    ├── auth/
    └── logger/

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Pluralization

Pluralize only collections.

❌ Bad

class ProgramsStore {
  constructor() {}
}

✔️ Good

class ProgramStore {
  constructor() {}
}

✔️ Good

customers.forEach((customer) => {
  ...
});

Use singularPlural for a list of a single property. [+]

✔️ Good

const programs = [{
  id: 1,
}, {
  id: 2,
}];

const program = programs[0];
const programId = 1;
const programIds = [1, 2];

Use pluralOfSingular for a list of single item list.

✔️ Good

const program = {
  topics: ['addons'],
};

const topicsOfProgram = ['addons'];

Use pluralOfPlural for a list of lists.

✔️ Good

const programs = [{
  topics: ['addons'],
}, {
  topics: ['skins'],
}];

const topicsOfPrograms = ['skins', 'addons'];

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Variables

camelCase for variables.

❌ Bad

const firstname = 'Benadryl';
const first_name = 'Benadryl';
const FIRSTNAME = 'Benadryl';
const FIRST_NAME = 'Benadryl';

✔️ Good

const firstName = 'Benadryl';

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Acronyms

UPPERCASE for acronyms.

Names are for readability, not to appease a computer algorithm. [+]

❌ Bad

const { XMLHttpRequest } = require('...');

const xmlHttpRequest = { ... };

function requestIpAddress() {
  ...
}

function dbmxmlParse() {
  ...
}

✔️ Good

const { XMLHTTPRequest } = require('...');

const xmlHTTPRequest = { ... };

function requestIPAddress() {
  ...
}

function dbmXMLParse() {
  ...
}

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Abbreviations

camelCase for abbreviations.

❌ Bad

const programID = 0; // Id[entifier].
const isEXEFile = true; // Exe[cutable].
const androidAPPName = 'Zoom'; // App[lication].

✔️ Good

const programId = 0; // Id[entifier].
const isExeFile = true; // Exe[cutable].
const androidAppName = 'Zoom'; // App[lication].

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Verbosity

Avoid use of abbreviations for naming—be verbose.

❌ Bad

const accBalInSaving = 0;
const dmgPerSec = 100;

✔️ Good

const accountBalanceInSavings = 0;
const damagePerSecond = 100;

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HashMaps

keyToValue or valueByKey for HashMaps.

No rules for keys naming.

❌ Bad

const mapStateCounty = {
  CA: 58,
};

const numberOfCountiesIn = {
  CA: 58,
};

const countyCountOf = {
  CA: 58,
};

✔️ Good

const stateToCountiesCount = {
  CA: 58,
};

const countiesCountByState = {
  CA: 58,
};

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Constants

UPPERCASE for constants.

Constants are string or integer literals, used as aliases for “hard-coded” values.

✔️ Good

const SECONDS = 60;
const MINUTES = 60;
const HOURS = 24;
const DAY = SECONDS * MINUTES * HOURS;
const DAYS_UNTIL_TOMORROW = 1;

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Booleans

Use affirmative names.
Use is, are, have, has, can, should or any other prefix which indicates a yes or no as response. [+]

❌ Bad
```
const isUsersLoggedIn = true;
```
✔️ Good
```
const isEachUserLoggedIn = true;
```

Use affirmative names.

❌ Bad

const isNotActive = true;

if (!isNotActive) {
  ...
}

✔️ Good

const isActive = true;

if (isActive) {
  ...
}

Use convenient name when the boolean is optional with negative default value. [+]

Avoid double negatives.

Implicit default.

❌ Bad
```
function createWidget(isEnabled = true) {
  ...
}
```
✔️ Good
```
function createWidget(isDisabled) {
  ...
}
```

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Contextualization

Do not add redundant context to variable names when the context is already provided by the containing object or class. [+]

❌ Bad

const product = {
  productId: "XXX-XXX",
  productName: "book",
};

product.userId;

✔️ Good

const user = {
  id: "XXX-XXX",
  name: "book",
};

product.id;

Do not contextualize the naming of the provided arguments to the functions.

Easier perform massive find or replace.

❌ Bad

function findProgramById(id) {
  ...
}

const programId = 'XXXX-XXXX';

findProgramById(programId);

✔️ Good

function findProgramById(programId) {
  ...
}

const programId = 'XXXX-XXXX';

findProgramById(programId);

❌ Bad

function findProgramById({ id }) {
  ...
}

const programId = 'XXXX-XXXX';

findProgramById({ id: programId });

✔️ Good

function findProgramById({ programId }) {
  ...
}

const programId = 'XXXX-XXXX';

findProgramById({ programId });

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Timestamps

Use verbAt.

✔️ Good

const createdAt = new Date().toISOString();
const updatedAt = new Date().toISOString();

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Functions

camelCase for functions.
Recommended use verbAdjectiveContextStructureHow pattern, where verb stick to action, adjective act as modifier for a context, and context is the object being interacted with. Adjective, context, structure and how are optionals. [+]

❌ Bad
```
function programGetActiveById(programId) {
  ...
}
```
✔️ Good
```
function findActiveProgramById(programId) {
  ...
}
```
Skip get prefix when function is returning a boolean.

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Vocabulary

Prefix	Description
`to`	Convert object to another type.
`plus`	Returns a copy object with the amount added.
`minus`	Returns a copy object with the amount subtracted.
`with`	Return a copy with element target.
`of`	Returns an instance where the factory is primarily validating the input parameters, not converting them.
`from`	Converts the input parameters to an instance of the target object, which may involve losing information from the input.
`parse`	Parses the input string to produce an instance of the target class.
`format`	Uses the specified formatter to format the values in the temporal object.
`at`	Combines this object with another.
`get`	Return a part of the state of the object.
`list`	Return a collection of part of the state of the object.
`create`	Returns a new instance on each invocation.
`build`	Returns a new instance where many separate pieces of information are combined in some way.
`generate`	Returns a new instance where a calculation is used to produce a value from an input.

^{Partial borrowed from oracle documentation. [+]}

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Constructors

PascalCase for constructors.

✔️ Good

class GoodGreeter {
  name;

  constructor() {
    this.name = 'hello';
  }
}

Where appropriate, use a compound word for the naming. The second part of the derived name can be the name of the pattern. [+]

✔️ Good
```
class GetItemBySlugUseCase {
  constructor() {}
}
```

Infer context on naming class methods.

❌ Bad

class ProgramStore {
  getProgramById(programId) {
    ...
  }
}

✔️ Good

class ProgramStore {
  getById(programId) {
    ...
  }
}

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Enumerations

PascalCase for enumerations and value names. [+]

Singular type name.

Enumerations are used to represent a fixed number of possible values.

❌ Bad

const codes = {
  notFound: 'NotFound',
  badRequest: 'BadRequest',
};

✔️ Good

const Code = {
  NotFound: 'NotFound',
  BadRequest: 'BadRequest',
};

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Measures

Use measures as suffix.

❌ Bad

const REQUEST_TIMEOUT = 2000;
const MIN_COMPRESSION = 64;

✔️ Good

const REQUEST_TIMEOUT_MS = 2000;
const MIN_COMPRESSION_BYTE = 64;

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Counts

Use count as suffix to indicate quantity. [+]

count is shorter than numberOf.

number is ambiguous. It could be a count, or an index, or some other number.

Use index as suffix to indicate sequence number 0..n.

❌ Bad

const MAX_PROGRAMS = 5;
const PROGRAM_NUMBER = 2;

✔️ Good

const MAX_PROGRAM_COUNT = 5;
const PROGRAM_INDEX = 2;

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Public modules

Don’t use descriptive names for public modules.

Descriptive names are anti-democratic. [+].

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Asynchronous

Use sync suffix for synchronous function when you have asynchronous version of the same function.

NodeJS implicit convention. [+]

Use when prefix for variables. [+]

It sounds like the Promise then method.

It should mean ‘when this happens’.

✔️ Good

async function listPrograms() {
  ...
}

const whenPrograms = listPrograms();
const programs = await whenPrograms;

❌ Bad

function listPrograms() {
  ...
}

async function listProgramsAsync() {
  ...
}

const whenPrograms = listProgramsAsync();
const programs = await whenPrograms;

✔️ Good

function listProgramsSync() {
  ...
}

async function listPrograms() {
  ...
}

const whenPrograms = listPrograms();
const programs = await whenPrograms;

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Generators

Use gen suffix when you have Generator version of the same function.

Use iter prefix for variables. [+]

❌ Bad

function* listProgramsGen() {
  ...
}

const iterPrograms = listProgramsGen();

✔️ Good

function* listPrograms() {
  ...
}

const iterPrograms = listPrograms();

✔️ Good

async function listPrograms() {
  ...
}

async function* listProgramsGen() {
  ...
}

const iterPrograms = listProgramsGen();
const programs = [];

for await (let program of iterPrograms) {
  programs.push(program);
}

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Formatting conventions

Curly braces

Delimit scope blocks with curly braces. [+]
Opening brace goes on the end of the current line, and the last brace in the new line.

Known as egyptian brackets. [+]

❌ Bad
```
if (true) doSomething();
```
✔️ Good
```
if (true) {
  doSomething();
}
```

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Block scopes

Space between block scopes.

❌ Bad

if (true) {
  doSomething();
}
if (true) {
  doSomethingElse();
}

✔️ Good

if (true) {
  doSomething();
}

if (true) {
  doSomethingElse();
}

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Programming practices

Be consistent with existing code.

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Exports

Use named exports.

To avoid interoperational problems between ES Modules and CommonJS. [+]

❌ Bad
```
export default class MyClass {
  ...
}
```
✔️ Good
```
export class MyClass {
  ...
}
```

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Functions

Use function syntax for functions.

In general function syntax is preferred, in particular for top level functions (to avoid TDZ issues, export const foo = () => {} function will not be available to be called unless the module where it came from has already been evaluated, otherwise you'll get the temporal dead zone error, happens with circular dependencies). [+]
Use arrow functions for callbacks.

Arrow syntax should be limited to closures.

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Decorations

Avoid use of annotations for decorations.

Are executed at time of interpretation, that could create inconvenience when you are injecting dependencies which need be initialized at tame of class instance creation (e.g.: happens on resolving with auto-wire).

❌ Bad
```
class MyClass {
  @decorate()
  doStuff() {
    ...
  }
}
```
✔️ Good
```
class MyClass {
  constructor() {
    this.doStuff = decorate(this.doStuff);
  }

  doStuff() {
    ...
  }
}
```

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Interfaces

Use interfaces over aliases where possible.

❌ Bad

type FnAsync = (...args: any[]) => Promise<any>;

✔️ Good

interface FnAsync {
  (...args: any[]): Promise<any>;
}

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Constructors

Use classes if you have more than one method and shared state.

❌ Bad

class RedisClient {
  constructor(baseURL) {
    ...
  }

  create() {
    ...
  }
}

const redisClient = new RedisClient(baseURL);
const cacheClient = redisClient.create();

✔️ Good

function createRedisClientCreator(baseURL) {
  return function createRedisClient() {
    ...
  }
}

const createRedisClient = createRedisClientCreator(baseURL);
const cacheClient = createRedisClient();

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Monorepos

Every package should contain all the needed dependencies.

Doing this allows us to cleanly decouple projects (packages) from one another, since you don't have to merge all their dependencies in one huge unmaintainable list. [+]

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Comments

Comments are code smell, when comment describes what the code is doing.

From a philosophical point of view, each line of code contains a technical debt for further support. Only the final functionality is the value. And if you can implement it without a single line (of commentary) at all, then everything is perfect. Otherwise, you should always have the WHY / WHY motive you added it for. Theoretically, this motive should be indicated in the commentary. The WHAT question is usually resolved by meaningful of the identifiers of classes, functions and variables. The question HOW should be clear from the code itself (also theoretically). [+] [++]

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Composition

Use composition over inheritance.

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Goal

If we start from the fact that programming is a chain of taking decisions, the aim of this guide is to inspire you and facilitate to take such decisions.

Following guide is a set of different sources most of them conveniently linked.

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Other projects

Daisugi is a minimalist functional middleware engine.
Kintsugi is a set of utilities to help build a fault tolerant services.
Kado is a minimal and unobtrusive inversion of control container.
Oza is a fast, opinionated, minimalist web framework for NodeJS.

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License

MIT

Name		Name	Last commit message	Last commit date
Latest commit History 6 Commits
LICENSE		LICENSE
README.md		README.md
guide1.js		guide1.js
guide2.ts		guide2.ts

License

daisugiland/javascript-style-guide

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JavaScript style guide

Table of contents

Naming conventions

Folders and files

Pluralization

Variables

Acronyms

Abbreviations

Verbosity

HashMaps

Constants

Booleans

Contextualization

Timestamps

Functions

Vocabulary

Constructors

Enumerations

Measures

Counts

Public modules

Asynchronous

Generators

Formatting conventions

Curly braces

Block scopes

Programming practices

Exports

Functions

Decorations

Interfaces

Constructors

Monorepos

Comments

Composition

Goal

Other projects

License

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