Basics

This tutorial assumes you have a basic understanding of JavaScript. If you are just getting started, it is a good idea to read the JavaScript tutorial first.

Every valid JavaScript file is a valid TypeScript file.

TypeScript adds some really useful features to JavaScript, but the JavaScript interpreter running in your web browser or in Node.js can't understand them. To run a TypeScript program, a build system converts it into JavaScript.

The TypeScript compiler converted the program above into the standard JavaScript program below.

function greet(name) {
    console.log(`Hello, ${name}!`);
}
const age = greet('Alice Smith');

Normally, you would write TypeScript code with a modern editor like VSCode.

Variables

There are three ways to define a variable in TypeScript.

Questions

Strings

A JavaScript string represents a sequence of characters, like "Hello" or "42".

This is another test

Numbers

JavaScript does not have a special runtime value for integers, so there is no equivalent to int or float in languages like Java and C++. Everything is simply number.

Infinity and NaN

JavaScript has special values to represent infinity (Infinity) and "not a number" (NaN).

A common situation where NaN arises in TypeScript programs is during the conversion of a string value to number.

Booleans

A boolean value is either true or false.

Arrays

An array is a sequence of values. To specify the type of an array like [1, 2, 3], you can either use number[] or Array<number>.

Tuples

A tuple is an exact sequence of values.

Notice that you will get a tuple error if the specified sequence is not matched exactly.