TypeScript — Basics

What is TypeScript?

TypeScript extends javascript by adding types

Why TypeScript?

TypeScript simplifies javascript code making it easier to read and write

Basic datatypes:

Number :

In typescript all integer and floats comes under numbers

Eg: let sum: number = 40;

String :

Single quotes and double quotes all are comes under string

Eg: let response: string = “success”;

Boolean :

It contains true/false value

Eg: let isCorrect: boolean = yes;

Object :

Object is type that represents non-primitive types, any thing that is not number, string, boolean, undefined etc

Eg: let person = { name : “john”, age : 29 }

Array :

Array is group of elements, we can define two ways

Eg: let marks: number[]= [45,56,56,76,67]

Eg: let students: string[] = [“john”,”jack”,”krish”]

Eg: let marks: Array<number> = [54,54,54,54]

Tuple :

It is an array with fixed number of elements whose types are known, but need not be same.

Eg: let studentResult : [number, string];

studentResult = [101,”john”];

Any :

Sometimes we do not know what will be the return value in that case we will use any

Eg: getResult(input: string) : any { return input + 2; }

Void :

It is opposite to any, mostly will see void in function return type. if any function does not return any value in that case we will use void

Eg: displayResult(input: string) : void { console.log(‘display result is’,input); }

Union ( | ) :

It is combine any datatypes or objects etc

Eg1: let result : number | string;

Here we can store both number and string values in result variable using union type.

Eg2: Below function take input as number, string or boolean.

union types

Enums :

It allows developer to define set of named constraints, it provides both numeric and string based enums.

enums

Above Colors default RED will take 0, GREEN =1, BLUE =2 etc

Also we can initialize with default value, for eg if you give RED = 5 then GREEN take 6, BLUE =7 etc.

And also we can give custom values.

enum-numbers

String enum are similar concept, In a string enum, each member has to be constant-initialized with a string literal, or with another string enum member.

Type :

By using type we can create custom type like below

type keyword

Function Type :

TypeScript functions can be created both as a named function or as an anonymous function.

function type

A function’s type has the same two parts: the type of the arguments and the return type. When writing out the whole function type, both parts are required.

function type

Function Callbacks:

Thanks for reading