JavaScript - Data Structures, Modern Operators and Strings

Destructuring Arrays

Switch the two variables.

[main, secondary] = [secondary, main]

const [p, q, r] = [8, 9];
console.log(p, q, r);

get r = undefined

Destructuring Objects

Set a default value

const { menu = [], starterMenu: starters = [] } = restaurant;
console.log(menu, starters);

Mutating Variables

let a = 111;
let b = 999;
const obj = { a: 23, b: 6, c: 234 };
({ a, b } = obj); // { } means code block
console.log(a, b);

{} means code block

Needs to wrap the destructuring assignment into parenthesis.

const restaurant = {
	orderDelivery: function ({ starterIndex, mainIndex, time }) {
	    console.log(
	      `Order received! ${this.starterMenu[starterIndex]} will be delivered at ${time}`
	    );
	  },
}
restaurant.orderDelivery({
  starterIndex: 1,
  mainIndex: 1,
  time: '22:40',
});

The Spread Operator

The spread operator ...arr takes all the elements from the array and it doesnt create new variables.

Only use it in places.

Copy Array

const mainMenuArray = [...restaurant.mainMenu]

Merge Arrays

const menu = [...restaurant.starterMenu, ...restaurant.mainMenu]

REST Pattern and Parameters

const [a, b, ...others] = [1, 2, 3, 5];

The rest patter always must be the last element in the array.