学习typescript- Basic Types

1.typescript基本声明类型有多少个种?分别怎么声明?

• Boolean

let isDone:boolead = false;

• Number(不管是所有类型,浮点数,2进制,16进制,统一为number)

let Num:number = 6; 

• String

let color:sring = "blue";

• Array

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

• Tuple

let x:[string,number];
x = ['22',22]  //ok
x = [22,'22'] //ok
x = ['sss', 222, 333, 'ssss']; //ok
x = ['sss', 222, 333, 'ssss',true]; //err

• Enum

enum Color {Red, Green, Blus}  //default 0 ,1 ,2
let c: Color = Color.Green;  //ok
let c: Color = 222; //err

enum Color {Red=1, Green, Blus}
let c: Color = Color.Green; //2

enum Color {Red=1, Green=4, Blus}
let c: Color = Color.Green; //2

enum Color {Red = 1, Green, Blus}
let c: string = Color[2]; //Green

• Any

let a:any = 4;   //ok
a = 'string';    //ok
a = true;       //ok
a = {};         //ok
a = [];         //ok
a = function () {
    //ok
};
const arr:any[] = [1,'1',true,{}]; //ok

• void

const fn = function ():void{
    true        //ok
};

const fn = function ():void{
    return 2      //err
};

let a:void = undefined; //ok
let a:void = null; //ok

• Undefined and Null

let a:undefined = null;   //ok
let a:undefined = undefined;   //ok
let a:null = undefined;   //ok
let a:null = null;   //ok

• never

//用于永远不会走到最后或者retrun error
function error(message: string): never {
    throw new Error(message);  
}

function fail() {
    return error("Something failed");
}

function infiniteLoop(): never {
    while (true) {
    }
}

• object

const obj:object = null; //ok
const obj:object = {};   //ok

• type assertions(断言)

let obj = {};
let num:number = obj ; //err

let obj = {};
let num:number = obj as number ; //ok
let num:number = <number>obj ; //ok