JavaScript cheat sheet

cheatsheet.js

// Random 0 to max (excl)
const random = (max) => Math.floor(Math.random() * max)
// Random between (min incl, max excl)
const random = (min, max) => Math.floor(Math.random() * (max - min) + min)

// Fill array
const arr = new Array(42).fill(0).map(() => random(1, 5))

// Remove duplicates from Array (tip: fallback using indexOf)
let chars = ['A', 'B', 'A', 'C', 'B']
let uniqueChars = [...new Set(chars)]

// Empty an array
A.length = 0 // A.splice(0) or A.splice(0, A.length)

// Remove/replace element from array in place
[1, 2, 3, 4].splice(1, 1, 42) // returns item (2) -> [1, 42, 3, 4]

// Shallow copy portion of array
[1, 2, 3, 4].slice(2) // returns from index to end [3, 4]

// Date add
Date.now() + 1000 * 60 * x  // x minutes
Date.now() + 1000 * 60 * 60 * x // x hours
Date.now() + 1000 * 60 * 60 * 24 * x // x days

// Even/odd numbers
for (let i = 0; i < 10; i++)
  i % 2 // even === 0

// Divisible by 3
1 % 3 === 0  // 1 false
2 % 3 === 0  // 2 false
3 % 3 === 0  // 0 true

// Sort is in-place and by default uses UTF-16 code order
// sort by value (numeric)
[0, 3, 1, 2].sort((a, b) => a - b)
// case insensitive sort by name (string)
['AbE', 'Ben', 'aBe'].sort((a, b) => {
  const nameA = a.toUpperCase(); // ignore upper and lowercase
  const nameB = b.toUpperCase(); // ignore upper and lowercase
  if (nameA < nameB) return -1;
  if (nameA > nameB) return 1;
  return 0; // names must be equal
});

// Fetch
fetch('https://...', {
  method: 'post',
  headers: {
    'Content-Type': 'application/json'
    // 'Content-Type': 'application/x-www-form-urlencoded',
  },
  body: JSON.stringify({ asdf: 42 })
})