Primitive types in TypeScript

  • 5 minutes

Let's start by reviewing the most basic and common types you might encounter when writing JavaScript or TypeScript code. These basic types will later form the core building blocks of more complex types.

Boolean type

The most basic datatype is the true or false value, known as a boolean.

For example:

let flag: boolean;
let yes = true;
let no = false;

Number and BigInteger types

As in JavaScript, all numbers in TypeScript are either floating point values or BigIntegers. These floating-point numbers get the type number, while BigIntegers get the type bigint. In addition to hexadecimal and decimal literals, TypeScript also supports binary and octal literals introduced in ECMAScript 2015.

For example:

let x: number;
let y = 0;
let z: number = 123.456;
let big: bigint = 100n;

String type

The string keyword represents sequences of characters stored as Unicode UTF-16 code units. Like JavaScript, TypeScript also uses double quotes (") or single quotes (') to surround string data.

Some examples:

let s: string;
let empty = "";
let abc = 'abc';

In TypeScript, you can also use template strings, which can span multiple lines and have embedded expressions. These strings are surrounded by the backtick/backquote (`) character, and embedded expressions are of the form ${ expr }.

For example:

let firstName: string = "Mateo";
let sentence: string = `My name is ${firstName}.
    I am new to TypeScript.`;
console.log(sentence);

This example produces the output:

My name is Mateo.
    I am new to TypeScript.

The void, null, and undefined types

JavaScript and TypeScript have two primitive values used to signal absent or uninitialized value: null and undefined. These types are most useful in the context of functions, so we'll discuss them in more detail in a later module.