Javascript snippets you need to know right now - 3

const average = (...nums) => nums.reduce((acc, val) => acc + val, 0) / nums.length;average(...[1, 2, 3]); // 2average(1, 2, 3); // 2

const averageBy = (arr, fn) =>  arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0) /  arr.length;averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 5averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 5

const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());capitalizeEveryWord('hello world!'); // 'Hello World!'

const fs = require('fs');const createDirIfNotExists = dir => (!fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined);createDirIfNotExists('test'); // creates the directory 'test', if it doesn't exist

const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]

const difference = (a, b) => {  const s = new Set(b);  return a.filter(x => !s.has(x));};difference([1, 2, 3], [1, 2, 4]); // [3]

const differenceBy = (a, b, fn) => {  const s = new Set(b.map(fn));  return a.filter(x => !s.has(fn(x)));};differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]

const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1);differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2]

const digitize = n => [...`${n}`].map(i => parseInt(i));digitize(431); // [4, 3, 1]

const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);distance(1, 1, 2, 3); // 2.23606797749979