npm JavaScript

Neil Haddley • February 25, 2021

Create and publish an npm module using JavaScript.

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Recursion

When a function is called, the computer must "remember" the place it was called from... so that it can return to that location with the result once the call is complete. Typically, this information is saved on the call stack... For tail calls, there is no need to remember the caller...

https://en.wikipedia.org/wiki/Tail_call

Some interpreters (and compilers) eliminate the stack frame creation and destruction work when they recognize tail recursion.

JavaScript

Create a folder for the new node module.

$ mkdir haddley-factorial-js

Navigate to the new folder

$ cd haddley-factorial-js

Create a package.json file

$ npm init -y

Image Description

Image Description

Mocha and Chai

Automated testing is added using mocha and chai.

$ npm i --save-dev mocha

$ npm i --save-dev chai

$ mkdir test

npm test

npm test

package.json

This is final package.json file

Github actions

Github actions ensure that testing is performed using multiple versions of node.

Tests are running

Tests are running

Code passed all of the provided tests

Code passed all of the provided tests

Test results for multiple versions of node

Test results for multiple versions of node

Publishing to npmjs.com

To publish the module to npmjs.com

$ node login

$ node publish

npm publish

npm publish

index.js

JAVASCRIPT
1const factorial = (n) => {
2    if (n < 2) return 1;
3    return n * factorial(n - 1);
4}
5
6exports.factorial = factorial
7
8const factorial_tr = (n) => {
9
10    function fact(n, acc) {
11        if (n < 2) return acc;
12        return fact(n - 1, n * acc);
13    }
14
15    return fact(n, 1)
16}
17
18exports.factorial_tr = factorial_tr
19
20const factorial_it = (n) => {
21
22    let acc = 1
23
24    for (i = n; i > 1; i--) {
25        acc = acc * i
26    }
27
28    return acc
29}
30
31exports.factorial_it = factorial_it

testtest.js

JAVASCRIPT
1var module = require('../index')
2var expect = require('chai').expect;
3
4describe('#factorial()', function () {
5
6    // test recursive function
7    it('should calculate factorial of 9 using recursion', function () {
8        // add an assertion
9        expect(module.factorial(9)).to.equal(362880);
10    })
11
12    // test tail recursion version
13    it('should calculate factorial of 9 using tail recursion', function () {
14        // add an assertion
15        expect(module.factorial_tr(9)).to.equal(362880);
16    })
17
18    // test iteration version
19    it('should calculate factorial of 9 using iteration', function () {
20        // add an assertion
21        expect(module.factorial_it(9)).to.equal(362880);
22    })
23
24    // test tail recursion version
25    it('should calculate factorial of 170 using recursion', function () {
26        // add an assertion
27        expect(module.factorial(170)).to.equal(7.257415615307994e+306);
28    })
29
30    // test tail recursion version
31    it('should calculate factorial of 170 using tail recursion', function () {
32        // add an assertion
33        expect(module.factorial_tr(170)).to.equal(7.257415615308004e+306);
34    })
35
36    // test iteration version
37    it('should calculate factorial of 170 using iteration', function () {
38        // add an assertion
39        expect(module.factorial_it(170)).to.equal(7.257415615308004e+306);
40    })
41
42    // test tail recursion version
43    it('should calculate factorial of 171 using recursion', function () {
44        // add an assertion
45        expect(module.factorial(171)).to.equal(Infinity);
46    })
47
48    // test tail recursion version
49    it('should calculate factorial of 171 using tail recursion', function () {
50        // add an assertion
51        expect(module.factorial_tr(171)).to.equal(Infinity);
52    })
53
54    // test iteration version
55    it('should calculate factorial of 171 using iteration', function () {
56        // add an assertion
57        expect(module.factorial_it(171)).to.equal(Infinity);
58    })
59
60    // test recursive function
61    it('should calculate factorial of 10000 using recursion', function () {
62        this.timeout(10000);
63        // add an assertion
64        expect(module.factorial(10000)).to.equal(Infinity);
65    })
66
67    // test recursive function
68    it('should calculate factorial of 10000 using tail recursion', function () {
69        this.timeout(10000);
70        // add an assertion
71        expect(module.factorial_tr(10000)).to.equal(Infinity);
72    })
73
74    // test recursive function
75    it('should calculate factorial of 1600000 using iteration', function () {
76        this.timeout(10000);
77        // add an assertion
78        expect(module.factorial_it(1600000)).to.equal(Infinity);
79    })
80
81
82})

package.json

JAVASCRIPT
1{
2  "name": "haddley-factorial-js",
3  "version": "1.0.0",
4  "description": "",
5  "main": "index.js",
6  "scripts": {
7    "test": "mocha"
8  },
9  "repository": {
10    "type": "git",
11    "url": "git+https://github.com/Haddley/haddley-factorial-js.git"
12  },
13  "keywords": [],
14  "author": "",
15  "license": "ISC",
16  "bugs": {
17    "url": "https://github.com/Haddley/haddley-factorial-js/issues"
18  },
19  "homepage": "https://github.com/Haddley/haddley-factorial-js#readme",
20  "devDependencies": {
21    "chai": "^4.3.0",
22    "mocha": "^8.3.0"
23  }
24}

node.js.yml

JAVASCRIPT
1# This workflow will do a clean install of node dependencies, build the source code and run tests across different versions of node
2# For more information see: https://help.github.com/actions/language-and-framework-guides/using-nodejs-with-github-actions
3
4name: Node.js CI
5
6on:
7  push:
8    branches: [ main ]
9  pull_request:
10    branches: [ main ]
11
12jobs:
13  build:
14
15    runs-on: ubuntu-latest
16
17    strategy:
18      matrix:
19        node-version: [10.x, 12.x, 14.x, 15.x]
20        # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
21
22    steps:
23    - uses: actions/checkout@v2
24    - name: Use Node.js ${{ matrix.node-version }}
25      uses: actions/setup-node@v1
26      with:
27        node-version: ${{ matrix.node-version }}
28    - run: npm ci
29    - run: npm run build --if-present
30    - run: npm test