Handbook

1. Basic Types

//布尔
let isDone: boolean = false;

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

//字符串
let color: string = "blue";
color = 'red';

//模板
let fullName: string = `Bob Bobbington`;
let age: number = 37;
let sentence: string = `Hello, my name is ${ fullName }.

let sentence: string = "Hello, my name is " + fullName + ".\n\n" +
    "I'll be " + (age + 1) + " years old next month.";

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

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

console.log(x[0].substring(1)); // OK
console.log(x[1].substring(1)); // Error, 'number' does not have 'substring'
x[3] = "world"; // Error, Property '3' does not exist on type '[string, number]'.

console.log(x[5].toString()); // Error, Property '5' does not exist on type '[string, number]'.

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

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

//Any
let notSure: any = 4;
notSure = "maybe a string instead";
notSure = false; // okay, definitely a boolean

let list: any[] = [1, true, "free"];

list[1] = 100;

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

//object is a type that represents the non-primitive type, i.e. anything that is not number, string, boolean, bigint, symbol, null, or undefined.

//As
let someValue: any = "this is a string";

let strLength: number = (someValue as string).length;

2. 变量声明

var,let,const,解构