Ways I use destructuring in JS

destructuring.js

// basic destructuring
const { key1 } = { key1: 10 } // key1 = 10
const [x, y, z] = [1, 2, 3] // x = 1, y = 2, z = 3
const [head, ...tail] = [1, 2, 3] // head = 1, tail = [2, 3]
const { a: { b } } = { a: { b: 20 } } // b = 20

// storing value in a variable with a different name
const { key1: varForKey1 } = { key1: 20 } // varForKey1 = 20
const { 'quoted-key': x } = { 'quoted-key': 10 } // x = 10

// dependent default values part I
const { x, y = x } = { x: 20 } // x = 20, y = 20
const { x, y = x } = { x: { a: 20 } } // x and y point to same object { a: 20 }
const { x = 'test', y = x } = {} // x = 'test', y = 'test'

// dependent default values part II
function fn(x = 0, y = x, z = x) {
  // fn() -> 0 0 0
  // fn(10) -> 10 10 10
  // fn(10, 20) -> 10 20 10
  // fn(undefined, 9001) -> 0 9001 0
  console.log(x, y, z) 
}
// with some tasty currying
var fn = (x = 10) => (y = x) => console.log(x, y)

// enforce mandatory param
function mandatory() {
  throw new TypeError('Failed to provide a mandatory param')
}

function fn(mandatoryParam = mandatory()) {
  console.log(mandatoryParam)
}