Object Rest and Spread in TypeScript

Published on December 9, 2016

TypeScript

By Alligator.io

Developer and author at DigitalOcean.

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TypeScript 2.1 brings us object rest & spread to easily destructure, make shallow copies and merge objects into new ones.

Object Spread

Create shallow copy of objects:

const names = {cat: 'Bob', dog: 'Fred', alligator: 'Benedict'};

const newNames = { ...names };

console.log(newNames.cat); // Bob

You can merge multiple objects into a new object:

const names1 = {cat: 'Bob'};
const names2 = {dog: 'Fred', alligator: 'Benedict'};

const newNames = { ...names1, ...names2 };

console.log(newNames.alligator); // Benedict

You can add new properties too, along with using a spread:

const names = {cat: 'Bob', dog: 'Fred', alligator: 'Benedict'};

const newNames = { ...names, hamster: 'Jude' };

console.log(newNames.hamster); // Jude

Note that if a property ends up being inserted multiple times, the last one in wins:

const names = {cat: 'Bob', dog: 'Fred', alligator: 'Benedict'};

const newNames = { dog: 'Skip', ...names };

console.log(newNames.dog); // Fred

Object Rest

Similar to what we can already do in pure JavaScript with object destructuring, rest brings us something that’s in the pipelines for ES2017:

const names = {cat: 'Bob', dog: 'Fred', alligator: 'Benedict'};

const { cat, ...otherAnimals } = names;

console.log(cat); // Bob
console.log(otherAnimals); // {dog: 'Fred', alligator: 'Benedict'}