JavaScript Basics

By Xah Lee. Date: . Last updated: .

This page teaches you the basics of JavaScript, for beginners, in 30 minutes.

This tutorial teachs the ES2015 version of JavaScript.

ES2015 is a new JavaScript spec released in 2015, and is supported by all browsers now. It adds significant features to the language.

Running JavaScript

Comment

Printing

String

Semicolon can be omitted most of the time. When to insert semicolon is complex. For now, just follow examples in this tutorial. For detail, see Semicolon Rules.

Arithmetic

Assignment

Number

JavaScript doesn't have int/float distinction. They are just type “number”. It's similar to other language's “float”.

console.log(typeof 3 === "number");
console.log(typeof 3.2 === "number");
// true

Convert Decimal to Integer

to convert a number to integer.

console.log(Math.floor(3.5847) === 3);
console.log(Math.ceil(3.5847) === 4);

console.log(Math.round(3.54) === 4);
console.log(Math.round(3.55) === 4);

String/Number Conversion

Variables

Data Types

True and False

Logic Operators

Number Comparison Operators

If Then Else

Iteration; Loop

Array

Define Function

JavaScript Object

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