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Spread syntax (...)

The spread (...) syntax allows an iterable, such as an array or string, to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected. In an object literal, the spread syntax enumerates the properties of an object and adds the key-value pairs to the object being created.


const array = [1, 2, 3];
const obj = { ...array }; // { 0: 1, 1: 2, 2: 3 }

Destructuring

The destructuring syntax is a JavaScript syntax that makes it possible to unpack values from arrays, or properties from objects, into distinct variables. It can be used in locations that receive data (such as the left-hand side of an assignment or anywhere that creates new identifier bindings).


let a, b, rest;
[a, b] = [10, 20];

console.log(a);
// Expected output: 10

console.log(b);
// Expected output: 20

[a, b, ...rest] = [10, 20, 30, 40, 50];

console.log(rest);
// Expected output: Array [30, 40, 50]

const obj = { a, b, c };
const { a, b, c } = obj;
// Equivalent to:
// const a = obj.a, b = obj.b, c = obj.c;

Optional chaining (?.)

The optional chaining (?.) operator accesses an object's property or calls a function. If the object accessed or function called using this operator is undefined or null, the expression short circuits and evaluates to undefined instead of throwing an error.


const adventurer = {
name: "Alice",
cat: {
name: "Dinah",
},
};

const dogName = adventurer.dog?.name;
console.log(dogName);
// Expected output: undefined

console.log(adventurer.someNonExistentMethod?.());
// Expected output: undefined