Javascript Cheat Sheet

Comments

// Single line comment
/*
  Multi-line comment
*/

Var Keyword

var name = "John";

Const Keyword

const pi = 3.14;

Console

console.log("Hello, World!");

Let Keyword

let age = 25;

Variables

let name = "John";

Numbers

let x = 5;
let y = 3.14;

Strings

let greeting = "Hello, World!";

Block Scope

if (true) {
    let x = 5; // Block scope
}

Global Scope

var x = 5; // Global scope

Function Scope

function myFunction() {
    var x = 5; // Function scope
}

Arithmetic Operators

let x = 5 + 2; // Addition
let y = 5 - 2; // Subtraction

Assignment Operators

let x = 5;
x += 2; // x = x + 2

Comparison Operators

let isEqual = (5 == 5); // true

Ternary Operators

let result = (5 > 2) ? "True" : "False";

Logical Operators

let and = true && false; // false

Bitwise Operators

let bitwiseAnd = 5 & 1; // 1

If-Else Statement

if (true) {
    // code
} else {
    // code
}

Else-If Statement

if (x > 10) {
    // code
} else if (x > 5) {
    // code
} else {
    // code
}

Switch Statement

switch (x) {
    case 1:
        // code
        break;
    case 2:
        // code
        break;
    default:
        // code
}

For Loop

for (let i = 0; i < 5; i++) {
    // code
}

Continue

for (let i = 0; i < 5; i++) {
    if (i === 2) {
        continue;
    }
    // code
}

Break

for (let i = 0; i < 5; i++) {
    if (i === 2) {
        break;
    }
    // code
}

While Loop

let i = 0;
while (i < 5) {
    // code
    i++;
}

For...In Loop

let object = {a: 1, b: 2};
for (let key in object) {
    // code
}

Do...While Loop

let i = 0;
do {
    // code
    i++;
} while (i < 5);

For...Of Loop

let array = [1, 2, 3];
for (let value of array) {
    // code
}

Arrays and Index

let array = [1, 2, 3];
console.log(array[0]); // 1

.Concat() Method

let newArray = array.concat([4, 5]);

.Push() Method

array.push(4);

.Fill() Method

array.fill(0);

.Pop() Method

array.pop();

.Reverse() Method

array.reverse();

Declaring And Calling Function

function myFunction() {
    // code
}
myFunction();

Function With Parameter

function myFunction(param) {
    // code
}
myFunction("argument");

Return Keyword

function add(a, b) {
    return a + b;
}

Object

let object = {
    key: "value"
};

Dot Notation

object.key = "new value";

Bracket Notation

object["key"] = "new value";

Class

class MyClass {
    constructor() {
        // code
    }
}

Class Methods

class MyClass {
    myMethod() {
        // code
    }
}

Iterator

let iterator = array[Symbol.iterator]();

next() Method

iterator.next();

Modules

import { myFunction } from './myModule';

Export Multiple Objects

export { myFunction, myVariable };

Promises

let promise = new Promise((resolve, reject) => {
    // code
});

Catch() Method

promise.catch(error => {
    // code
});

Finally() Method

promise.finally(() => {
    // code
});

Async Function

async function myFunction() {
    // code
}

Await Keyword

let result = await myFunction();