Basics of TypeScript

Data Types

There are several data types in TypeScript. Here are some of them:

number,string,boolean,object,array,tuple,enum,any,void,null,undefined

Code Example

example.ts

let num: number = 5;
let name: string = "swayam";
let isTrue: boolean = true;
let obj: object = { name: "swayam", age: 20 };
let arr: number[] = [1, 2, 3, 4, 5];
let tuple: [string, number] = ["swayam", 20];
enum Color {
  Red,
  Green,
  Blue,
}

Arrays and Tuple

arraysandtuple.ts

let arr: number[] = [1, 2, 3, 4, 5];
let tuple: [string, number, bool] = ["Swayam", 22, true];
 
// If you use different data type in tuple, it will throw an error
 
let tuple: [string, number, bool] = ["Swayam", 22, "true"]; // Error
 
// Tuple array
 
let tupleArr: [string, number][] = [
  ["Swayam", 22],
  ["John", 25],
];

Union

union.ts

let name: string | number = "Swayam";
name = 22;

Note: You can use | to define multiple data types.

Enum

Enum is a way to store a set of constants. It is like an object with a set of key-value pairs.

enum.ts

enum Color {
  Red,
  Green,
  Blue,
}
 
let color: Color = Color.Red; // 0
color = Color.Green; // 1

Objects

objects.ts

const user: {
    name: string;
    age: number;
    hobbies: string[];
    mobileNumber: number;
} = {
    "name": "Swayam",
    "age": 22
    "hobbies": ["coding", "ping-pong"]
    "mobileNumber": 1234567890
}
 
console.log(user.name); // Swayam
log(user.hobbies); // ["coding", "ping-pong"]

Type

Another way to define objects is by using types.

types.ts

type User = {
    name: string;
    age: number;
    hobbies: string[];
    mobileNumber: number;
}
 
const user: User = {
    "name": "Swayam",
    "age": 22
    "hobbies": ["coding", "ping-pong"]
    "mobileNumber": 123456
}

Types are reusable and can be used in multiple places.

Interfaces

Interfaces are similar to types but they are more flexible.

interfaces.ts

interface User {
    name: string;
    age: number;
    hobbies: string[];
    mobileNumber: number;
}
 
const user: User = {
    "name": "Swayam",
    "age": 22
    "hobbies": ["coding", "ping-pong"]
    "mobileNumber": 123456
}

Difference between Types and Interfaces

Types	Interfaces
Can be used with primitive data types, unions, tuples, and more	Can only be used with objects
Can be used with `typeof`	Can be used with `extends`
Can be used with `keyof`	Can be used with `implements`

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