JavaScript Destructuring

Destructuring Assignment Syntax

The destructuring assignment syntax unpack object properties into variables:

let {firstName, lastName} = person;

It can also unpack arrays and any other iterables:

let [firstName, lastName] = person;

Object Destructuring

Example

// Create an Object
const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50
};

// Destructuring
let {firstName, lastName} = person;

The order of the properties does not matter:

Example

// Create an Object
const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50
};

// Destructuring
let {lastName, firstName} = person;

Note:

Destructuring is not destructive.

Destructuring does not change the original object.

Object Default Values

For potentially missing properties we can set default values:

Example

// Create an Object
const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50
};

// Destructuring
let {firstName, lastName, country = "US"} = person;

Object Property Alias

Example

// Create an Object
const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50
};

// Destructuring
let {lastName : name} = person;

String Destructuring

One use for destructuring is unpacking string characters.

Example

// Create a String
let name = "ScoolioAcademy";

// Destructuring
let [a1, a2, a3, a4, a5] = name;

Note:

Destructuring can be used with any iterables.

Array Destructuring

We can pick up array variables into our own variables:

Example

// Create an Array
const fruits = ["Bananas", "Oranges", "Apples", "Mangos"];

// Destructuring
let [fruit1, fruit2] = fruits;

Skipping Array Values

We can skip array values using two or more commas:

Example

// Create an Array
const fruits = ["Bananas", "Oranges", "Apples", "Mangos"];

// Destructuring
let [fruit1,,,fruit2] = fruits;

Array Position Values

We can pick up values from specific index locations of an array:

Example

// Create an Array
const fruits = ["Bananas", "Oranges", "Apples", "Mangos"];
// Destructuring
let {[0]:fruit1 ,[1]:fruit2} = fruits;

The Rest Property

You can end a destructuring syntax with a rest property.

This syntax will store all remaining values into a new array:

Example

// Create an Array
const numbers = [10, 20, 30, 40, 50, 60, 70];

// Destructuring
const [a,b, ...rest] = numbers

Destructuring Maps

Example

// Create a Map
const fruits = new Map([
  ["apples", 500],
  ["bananas", 300],
  ["oranges", 200]
]);

// Destructing
let text = "";
for (const [key, value] of fruits) {
  text += key + " is " + value;
}

Swapping JavaScript Variables

You can swap the values of two variables using a destructuring assignment:

Example

let firstName = "John";
let lastName = "Doe";

// Destructing
[firstName, lastName] = [lastName, firstName];