TypeScript



Feature



Basic Type

boolean

false and true.

    let a: boolean = false;





number

    let decimal: number = 6;
    let hex: number = 0xf00d;
    let binary: number = 0b1010;
    let octal: number = 0o744;



string

    let color: string = "blue";
    color = 'red';

array

    let list: number[] = [1, 2, 3];
    let list: Array<number> = [1, 2, 3];



tuple

    // Declare a tuple type
    let x: [string, number];
    // Initialize it
    x = ["hello", 10]; // OK
    // Initialize it incorrectly
    x = [10, "hello"]; // Error

enum

    enum Color {Red, Green, Blue}
    let c: Color = Color.Green;

any

    let isDone: any = false;
    isDone.ifItExists()

Why we need any? Would not specifying any word works? No. If without any the compiler shows that ifItExists is not a method of isDone.

This is a kind of compatible design? To get people comfortable.

void

It's like the opposite of any, that the variable cannot have any type. Useful in function return value.

    function warnUser(): void {
        console.log("This is my warning message");
    }

    let a: void = 1; //error
    let a: void = undefined; //pass

undefined & null

These two are actually a type???

It's in advanced topic chapter.



never

Never be assigned.

    let a:never;
    a = 2; // wrong

It's useful in function return type

    // Function returning never must have unreachable end point
    function error(message: string): never {
        throw new Error(message);
    }

object

Representing non-primitive type

Type Inference