Typescript

Implicit Type Declaration

let num = 10;        \\ Now the variable num can only store number values

Predefined Type for variables

const name: string;

Primitive Data Types

const number: number = 10;
const string: string = "Rishabh";
const boolean: boolean = true;

Array

const numbers = [1, 2, 3];
const numbers: number[];
const numbers: number[] = [1, 2, 3];

Union

const number: number | string = process.argv[2];
const bools: (number | boolean)[] = [0, true];

Objects -> Explicit declaration can only be done on let variables, const variables cannot be declare explicitly. Explicit declaration can be done used type or interface keyword.

// Implicit Declaration
const person : {
	name: 'Rishabh',
	age: 23
}

// Explicit Declaration
let person: {
	name: string;
	age: number;
}

person = {
	name: 'Rishabh'
	age: 23
}

Optional Variable -> When not sure about if the variable will be required in all scenarios.

let person: {
  name: string;
  age: number;
  phone: string;
};