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JavaScript Cheatsheet

Variables

var

Declares a variable (function scoped)

let

Declares a block variable

const

Declares a block constant

Data Types

String

Textual data

Number

Numeric data

Boolean

True or false

Array

List of values

Object

Key-value pairs

DOM Manipulation

document.getElementById()

Find element by ID

document.querySelector()

Find first matching element

element.innerHTML

Get or set HTML content

element.style.property

Change CSS style

Events

onclick

The user clicks an HTML element

onchange

An HTML element has been changed

onmouseover

The user moves the mouse over an HTML element

onkeydown

The user pushes a keyboard key