NI Dev Conference

Code and Slides for inaugural Northern Ireland Developer Conference talk https://www.nidevconf.com/

Slides from talk as Open Document Presentation file and PDF

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Step by step instructions to recreate kata.

Create new directory

mkdir ni_dev_conf

Change into the new directory

cd ni_dev_conf

Initialize

npm init

Example:

This utility will walk you through creating a package.json file.
It only covers the most common items, and tries to guess sensible defaults.

See `npm help json` for definitive documentation on these fields
and exactly what they do.

Use `npm install <pkg> --save` afterwards to install a package and
save it as a dependency in the package.json file.

Press ^C at any time to quit.
name: (ni_dev_conf)
version: (1.0.0)
description: node version of prime factors kata done by uncle bob at ndc 2014
entry point: (index.js) factorsOf.js
test command: node node_modules/.bin/mocha
git repository:
keywords: prime factors kata uncle bob nidevconf nidevconf17
author: Diarmaid McGowan
license: (ISC)
About to write to /home/diarmaid/ni_dev_conf/package.json:

{
  "name": "ni_dev_conf",
  "version": "1.0.0",
  "description": "node version of prime factors kata done by uncle bob at ndc 2014",
  "main": "factorsOf.js",
  "scripts": {
    "test": "node node_modules/.bin/mocha"
  },
  "keywords": [
    "prime",
    "factors",
    "kata",
    "uncle",
    "bob",
    "nidevconf",
    "nidevconf17"
  ],
  "author": "Diarmaid McGowan",
  "license": "ISC"
}


Is this ok? (yes)

Install mocha and chai as devDependencies

npm install --save-dev mocha chai or shorthand npm i -D mocha chai

Create test directory

mkdir test

Create empty test file

touch test/factorsOf_test.js

Open the folder in Visual Studio Code

You can download and install from https://code.visualstudio.com/

Start writing our first test

I am using chai for the BDD style http://chaijs.com/guide/styles/#expect http://chaijs.com/api/bdd/

const expect = require('chai').expect;

describe('Prime Factors calculator', function () {
  it('returns the prime factors of a given integer', function () {

  });
});

Run the test npm test or shorthand npm t

All pass as we don't have any assertions

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Add our first test

    expect(factorsOf(1)).to.eql([]);

Run the test npm test or shorthand npm t

It fails.

  1) Prime Factors calculator returns the prime factors of a given in
teger:
     ReferenceError: factorsOf is not defined

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Add require for our implementation file.

const factorsOf = require('./factorsOf');

Run the test npm test or shorthand npm t

It fails.

Error: Cannot find module 'factorsOf'

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Create empty implementation file

touch test/factorsOf.js Storing in the test directory for convenience.

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Run the test npm test or shorthand npm t

It fails.

  1) Prime Factors calculator returns the prime factors of a given in
teger:
     TypeError: factorsOf is not a function

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Add empty function to the implementation file

let factorsOf = _ => undefined;

Run the test npm test or shorthand npm t

It still fails - same error.

  1) Prime Factors calculator returns the prime factors of a given in
teger:
     TypeError: factorsOf is not a function

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Export the function

module.exports = factorsOf;

Run the test npm test or shorthand npm t

It fails - but we now have the error we were expecting.

  1) Prime Factors calculator returns the prime factors of a given in
teger:
     AssertionError: expected undefined to deeply equal []
      at Context.<anonymous> (test/factorsOf_test.js:6:29)

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We can now start TDD

test for 1

expect(factorsOf(1)).to.eql([]);

solution (replace undefined with empty array)

let factorsOf = _ => [];

module.exports = factorsOf;

---

test for 2

expect(factorsOf(2)).to.eql([2]);

solution Try this but it fails first test. We need a condition here.

let factorsOf = _ => [2];

module.exports = factorsOf;

Lets refactor a bit....

Accept a parameter (n) declare a variable and initialize to empty array return the array At least we ar passing the first tests again.

let factorsOf = (n) => {
  let factors = [];
  return factors;
}

module.exports = factorsOf;

Lets add condition and push 2 onto the array

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    factors.push(2);
  }
  return factors;
}

module.exports = factorsOf;

---

test for 3

expect(factorsOf(3)).to.eql([3]);

solution (Whats the absolute minimum keystrokes) change the constant 2 to variable n

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

---

test for 4

expect(factorsOf(4)).to.eql([2, 2]);

solution (we have nothing that will add two entries) add a check mod 2 and add 2 but fails first test

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    if (n % 2 === 0) {
      factors.push(2);
      n /= 2;
    }
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

We need to surround factors.push(n); with a condition Starting to sense a smell here

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    if (n % 2 === 0) {
      factors.push(2);
      n /= 2;
    }
    if (n > 1) {
      factors.push(n);
    }
  }
  return factors;
}

module.exports = factorsOf;

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test for 5, 6 and 7

expect(factorsOf(5)).to.eql([5]);
expect(factorsOf(6)).to.eql([2, 3]);
expect(factorsOf(7)).to.eql([7]);

solution (these work with solution for 4)

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test for 8

expect(factorsOf(8)).to.eql([2, 2, 2]);

solution (change if to while)

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    while (n % 2 === 0) {
      factors.push(2);
      n /= 2;
    }
  }
  if (n > 1) {
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

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test for 9

expect(factorsOf(9)).to.eql([3, 3]);

solution (There is nothing that inserts a 3) We are really seeing a pattern here.

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    while (n % 2 === 0) {
      factors.push(2);
      n /= 2;
    }
    if (n % 3 === 0) {
      factors.push(3);
      n /= 3;
    }
  }
  if (n > 1) {
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

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test for 27

expect(factorsOf(27)).to.eql([3, 3, 3]);

solution (same as for 2, we see engine developing) Rules re being broken.

let factorsOf = (n) => {
  let factors = [];
  if (n > 1) {
    while (n % 2 === 0) {
      factors.push(2);
      n /= 2;
    }
    while (n % 3 === 0) {
      factors.push(3);
      n /= 3;
    }
  }
  if (n > 1) {
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

---

Lets refactor

Add a divisor variable and initialize to 2

replace 2 with divisor in while loop

increment the divisor after the while

remove the while for 3

let factorsOf = (n) => {
  let factors = [];
  let divisor = 2;
  if (n > 1) {
    while (n % divisor === 0) {
      factors.push(divisor);
      n /= divisor;
    }
    divisor++;
  }
  if (n > 1) {
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

we need to change the if to while

let factorsOf = (n) => {
  let factors = [];
  let divisor = 2;
  while (n > 1) {
    while (n % divisor === 0) {
      factors.push(divisor);
      n /= divisor;
    }
    divisor++;
  }
  if (n > 1) {
    factors.push(n);
  }
  return factors;
}

module.exports = factorsOf;

no longer need that last if

let factorsOf = (n) => {
  let factors = [];
  let divisor = 2;
  while (n > 1) {
    while (n % divisor === 0) {
      factors.push(divisor);
      n /= divisor;
    }
    divisor++;
  }
  return factors;
}

module.exports = factorsOf;

I think that us done.

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lets refactor first while to a for

let factorsOf = (n) => {
  let factors = [];
  for (let divisor = 2; n > 1; divisor++) {
    while (n % divisor === 0) {
      factors.push(divisor);
      n /= divisor;
    }
  }
  return factors;
}

module.exports = factorsOf;

---

lets refactor the other while to a for

let factorsOf = (n) => {
  let factors = [];
  for (let divisor = 2; n > 1; divisor++) {
    for (; n % divisor === 0; n /= divisor) {
      factors.push(divisor);
    }
  }
  return factors;
}

module.exports = factorsOf;

Thanks us done.