JS Operators Cheat Sheet

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?.

Optional Chaining

Checks each part of the property chain; if any part is null or undefined, it immediately returns undefined instead of continuing.

// object with nested data
const user = { profile: { age: 30 } };

const result = user?.profile?.age;

// result: 30

??

Nullish Coalescing

Returns the right-hand value only when the left-hand value is null or undefined.

const value = null;
const result = value ?? 5;

// result: 5

??=

Nullish Assignment

Checks whether the left-hand value is null or undefined; if it is, the right-hand value is assigned to it. Otherwise, nothing changes.

let count = null;
count ??= 10;

// result: count = 10

||=

Logical OR Assignment

Assigns the right-hand value when the left-hand value is falsy (“”, 0, false, null, undefined).

let title = "";
title ||= "Untitled";

// result: title = "Untitled"

&&=

Logical AND Assignment

Assigns the right-hand value only when the left-hand value is truthy.

let isActive = true;
isActive &&= checkStatus();

// result: isActive now depends on checkStatus()

!!

Boolean Conversion

Converts any value into a strict boolean true or false.

const value = 0;
const result = !!value;

// result: false

&& / ||

Short-Circuit Evaluation

Returns one of the operands based on truthiness instead of just true or false.

const a = "hello" && "world";
const b = "" || "fallback";

// a: "world"
// b: "fallback"

…

Spread Operator

Expands an array or object into individual elements or properties.

const a = [1, 2];
const b = [3, 4];
const merged = [...a, ...b];

// merged: [1, 2, 3, 4]

…

Rest Operator

Collects the remaining arguments or items into a new array.

function sum(...nums) {
  return nums.reduce((a, b) => a + b, 0);
}

// sum(1, 2, 3) returns 6

~~

Double Tilde

Quickly truncates a number toward zero (similar to Math.trunc).

const result = ~~3.99;

// result: 3

,

Comma Operator

Evaluates each expression from left to right; earlier expressions run but are discarded, and only the value of the final expression is returned.

let x = (console.log("A"), 10);

// logs "A", then x becomes 10

void

void Operator

Evaluates an expression but always returns undefined.

const result = void 0;

// result: undefined

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