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Showing content from https://www.typescripttutorial.net/typescript-tutorial/typescript-types/ below:

TypeScript Types

Summary: in this tutorial, you’ll learn about the TypeScript types and their purposes.

What is a type in TypeScript

In TypeScript, a type is a convenient way to refer to different properties and functions that a value has.

A value is anything you can assign to a variable e.g., a number, a string, an array, an object, and a function.

For example, see the following value:

'Hello'Code language: JavaScript (javascript)

When you look at this value, you can say it is a string. This value has properties and methods that a string has.

For example, the 'Hello' value has a property called length that returns the number of characters:

console.log('Hello'.length); Code language: JavaScript (javascript)

It also has many methods like match(), indexOf(), and toLocaleUpperCase(). For example:

console.log('Hello'.toLocaleUpperCase()); Code language: JavaScript (javascript)

When you look at the value 'Hello' and describe it by listing the properties and methods, it would be inconvenient.

A shorter way to refer to a value is to assign it a type. In this example, you say 'Hello' is a string. Then, you know that you can use the properties and methods of a string for the value 'Hello'.

In conclusion, in TypeScript:

Types in TypeScript

TypeScript inherits the built-in types from JavaScript. TypeScript types are categorized into:

Primitive types

The following illustrates the primitive types in TypeScript:

Name Description string Represent text data. number Represent numeric values. boolean Have true and false values. null Have one value: null. undefined Have one value: undefined. It is the default value of an uninitialized variable. symbol Represent a unique constant value. Object types

Object types are functions, arrays, classes, etc. Later, you’ll learn how to create custom object types.

Purposes of types in TypeScript

There are two main purposes of types in TypeScript:

Examples of TypeScript types

The following example uses the querySelector() method to select the <h1> element:

const heading = document.querySelector('h1');Code language: JavaScript (javascript)

The TypeScript compiler knows that the type of heading is HTMLHeadingElement:

And it shows a list of methods for the HTMLHeadingElement type that heading can access:

If you try to access a property or method that doesn’t exist, the TypeScript compiler will show an error. For example:

Summary

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