Different types of typescript

1. Number :

   It is used for both integers and floating-point numbers representation.

let val1: number = 26;
let val2: number = 42;
// We can also use number without specifying it's type
// like - 
let val3 = 64;

2. String :

   It represents the sequence of characters (alphabet, digit, symbols) but with double quotes.

let name: string = "Lakshman76";
let greeting: string = `Namaste ${name}`;
name = 42; // Warning - attempts to re-assign the value to a different type

3. Boolean :

   It is used only to represent logical values - true and false.

const isLoggedIn: boolean = false;
const isActive: boolean = true;

4. Array :

   It is used to store multiple values of the same data type.

const names: string[] = ["Radha", "Krishna"];
const evens: number[] = [2, 4, 6, 8, 10];

const mix: (string | number)[] = [123, "RAM", 423, "hello"];
// 2D Array 
const numList: number[][] = [[1, 2, 3, 4], [5, 6, 7, 8]];

5. Tuple :

   A tuple is a typed array with a pre-defined length and type for each index.

const user: [string, number, boolean];
user = ["Laksh", 20, true]; // value should be in this order

6. Void :

   It is generally used in function return type when a function returns nothing.

function greeeting(msg: string): void {
    console.log(msg);
}
greeting("Welcome to TYPESCRIPT");

7. Undefined :

   It represents an undefined value or the value given to uninitialized variables.

let message;
console.log(message); // undefined
message = undefined;
console.log(message); // undefined

8. Null :

   It represents a null value or when an object doesn’t have any value.

let empty: null = null;
console.log(empty); // null

9. Any :

   If a variable is declared with any type, those variables can hold any type of value.

   NOTE:- It is recommended to not use any.

let value: any;
value = "Hello ji";
console.log(value); // Hello ji
value = 45;
console.log(value); // 45

10. Enum :

    It is used to define the set of constant values.

    By default, enums will initialize the first value to 0 and add 1 to each additional value:

enum count {
    zero,
    one,
    two,
    three,
    four,
}
const val: count = count.two;
console.log(val); // 2

enum anotherCount {
    zero = 5,
    one,
    two,
    three,
    four,
}
const val1: anotherCount = anotherCount.one;
console.log(val1); // 6

There are two types of enum - a) number b) string

1. Number :

   We can set the value of the first numeric enum and have it auto-increment from that. And also

   We can assign unique number values for each enum value, and then the values will not incremented automatically:

enum anotherCount {
    zero = 5,
    one,
    two,
    three,
    four,
}
const val1: anotherCount = anotherCount.one;
console.log(val1); // 6

enum StatusCodes {
  NotFound = 404,
  Success = 200,
  Accepted = 202,
  BadRequest = 400
}
console.log(StatusCodes.NotFound); // 404

2. String :

   Enum can also contain strings. This is more common than numeric enums, because of their readability and intent.

enum directions {
  North = 'North',
  East = "East",
  South = "South",
  West = "West"
};
console.log(directions.North); // North

11. Never :

    It represents values that never occur, such as a function that never returns or always throws an error.

function throwError(message: string): never {
  throw new Error(message);
}

12. Union :

    It allows a variable to hold more than one type of value.

let multiple: number | string;
multiple = 123;
console.log(multiple); // 123
multiple = "ABC";
console.log(multiple); // ABC

13. Type aliases :

    It is used to create custom types using the type keyword.

type User = {
  name: string;
  email: string;
  isActive: boolean;
};
const newUser: User = {
    name: "Laksh",
    email: "laksh@dev.com",
    isActive: true
}
console.log(newUser); // { name: "Laksh", email: "laksh@dev.com", isActive: true }