basic-types.md

Basic Types

Boolean

let isDone: boolean = false;

Number

let decimal: numer = 6;
let hex: number = 0x00d;
let binary: number = 0b1010;
let octal: number = 0o744;

String

let fullName: string = "Cirno";
let age: number = 9;
let sentence: string = `Hello, my name is ${fullName}.
I'll be ${age + 1} years old next month.`;

Array

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

Tuple

固定索引固定类型，且有顺序限制

let x: [string, number];
// 通过
x = ["hello", 10];
// 初始化失败
x = [10, "hello"];

访问索引外的元素使用联合类型

x[3] = "world"; // OK, 'string' can be assigned to 'string | number'
console.log(x[5].toString()); // OK, 'string' and 'number' both have 'toString'
x[6] = true; // Error, 'boolean' isn't 'string | number'

Enum

enum Color {
  Red,
  Green,
  Blue
}
let c: Color = Color.Green; // 1
// 可为第一个元素重新设置索引开始值
enum Color {
  Red = 1,
  Green,
  Blue
}
let c: Color = Color.Green; // 2
// 全部指定值
enum Color {
  Red = 1,
  Green = 2,
  Blue = 4
}
let c: Color = Color.Green; // 2

方便的反向映射获取枚举变量的名称

enum Color {
  Red = 1,
  Green,
  Blue
}
let colorName: string = Color[2]; // 'Green'

Any

可随意赋值任意类型，常用于接受第三方插件的回调数据

let notSure: any = 4;
notSure.ifItExists(); // okay, ifItExists might exist at runtime
notSure.toFixed(); // okay, toFixed exists (but the compiler doesn't check)

let prettySure: Object = 4;
prettySure.toFixed(); // Error: Property 'toFixed' doesn't exist on type 'Object'.

声明没有类型限制的数组

let list: any[] = [1, true, "free"];
list[1] = 100;

Void

类似 any，不是任何类型，常见于不返回值的函数

function warnUser(): void {
  alert("This is my warning message");
}

声明一个 void 类型是无效的，因为只能赋值为null或者undefied

let unusable: void = undefined;

Null and Undefined

仅能赋值为各自对应的类型

let u: undefined = undefined;
let n: null = null;