[TypeScript] Types in TypeScript & Why TypeScript

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Introduction

In this article, I will be talking about the types in TypeScript. This is the first post in my TypeScript Series, so I will be talking a little bit about what is TypeScript (TS), and why you need it.

According to TypeScript's website,

TypeScript is JavaScript with syntax for types.

If you have learned programming languages like Java, you would know that JavaScript is much easier but less straightforward. In Java, you need to set the data type when you declare a variable. On the other hand, JavaScript does not require you to do that.

let str = "Type is not specified!";

In TypeScript, your code will be more specific and less subject to errors.

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Type List

Basic Types in TypeScript:

• String

• Number

• Boolean

• Object

• Array

• Tuple

• Any

• Enum

• Never

• Void

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Types

When you declare a variable in TypeScript, you will be assigning types as well. It is always a variable name followed by a colon (:), then followed by the type.

let example: type = _____;

String

let str: string = "Hello TS!";

Number

let num: number = 10;

Boolean Expression

let isMarried: boolean = true;

Object

There are two(2) ways when you declare an object in TypeScript.

// Declaring an object type
let obj1: object = { name: "John Doe", age: 34 };

// Declaring an object type & giving types to each property. 
let obj2: { name: string, age: number} = {name: "John Doe", age: 34};

Array

There are two3) ways when you declare an array in TypeScript

// Assigning "string" type to all the elements
let brands: Array<string> = ["Goolge", "Microsoft", "Meta"];

// Another way of assigning the type
let brands: string[] = ["Goolge", "Microsoft", "Meta"];

Tuple

// Specifying each element's type
let address: [string, number] = ["New York", 5276];

Any

// "any" type is available
let str: any = "Any type is available.";
let num: any = 10;
let isMarried: any = true;

Enum

You might have heard of this type if you have learned Java.

enum Brands { "Google", "Microsoft", "Meta" }
let brand: enum = Brands.Google;
let brand: enum = Brands[0];

Never

function myFunc(): never {
    while (true) {
    }
}

You can give the return type of a function by putting the colon (:) followed by the type.

If you know Java:

public int sum(int a, int b) {
    return a + b;
}

sum() must return an integer.

Void

A void type can be assigned when you declare a variable or function, but it has different usages.

Variable Declaration:

let var1: void = undefined;
let var2: void = null;

Void type can only contain either undefined or null.

Function Declaration:

function myFunc(): void {
    console.log("No return value.");
}

When you use it for the function's return type, void type means that you will not return anything.

In Java, you would do:

public void sayName() {
    console.log("John Doe");
}