Basic Types

Boolean

The most basic data type is the simple true/false value, which JavaScript and TypeScript call a boolean value.

let isDone: boolean = false;Try

Number

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.

let decimal: number = 6;
let hex: number = 0xf00d;
let binary: number = 0b1010;
let octal: number = 0o744;
let big: bigint = 100n;Try

String

Another fundamental part of creating programs in JavaScript for webpages and servers alike is working with textual data. As in other languages, we use the type string to refer to these textual datatypes. Just like JavaScript, TypeScript also uses double quotes (") or single quotes (') to surround string data.

let color: string = "blue";
color = 'red';

Template string

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 }.

let fullName: string = `Bob Bobbington`;
let age: number = 37;
let sentence: string = `Hello, my name is ${fullName}.

I'll be ${age + 1} years old next month.`;

Array

TypeScript, like JavaScript, allows you to work with arrays of values. Array types can be written in one of two ways. In the first, you use the type of the elements followed by [] to denote an array of that element type:

let list: number[] = [1, 2, 3];Try

The second way uses a generic array type, Array<elemType>:

let list: Array<number> = [1, 2, 3];

Tuple

Tuple types allow you to express an array with a fixed number of elements whose types are known, but need not be the same. For example, you may want to represent a value as a pair of a string and a number:

// Declare a tuple type
let x: [string, number];
// Initialize it
x = ["hello", 10]; // OK
// Initialize it incorrectly
x = [10, "hello"]; // Error
Type 'number' is not assignable to type 'string'.
Type 'string' is not assignable to type 'number'.

When accessing an element with a known index, the correct type is retrieved:

// OK
console.log(x[0].substring(1));
console.log(x[1].substring(1)); 
Property 'substring' does not exist on type 'number'.

Enum

A helpful addition to the standard set of datatypes from JavaScript is the enum. As in languages like C#, an enum is a way of giving more friendly names to sets of numeric values.

enum Color {
    Red,
    Green,
    Blue, 
} 

let c : Color = Color.Green;