interface
- 在接口中定义方法
定义传入参数和返回的类型
interface Counter {
(start: number): string;
interval: number;
reset(): void;
}
-
interface的合并
与类型别名不同，接口可以定义多次，会被自动合并为单个接口。
interface Point { x: number; }
interface Point { y: number; }
const point: Point = { x: 1, y: 2 };
断言
用<>或者as
let someValue: any = "this is a string";
let strLength: number = (<string>someValue).length;
let strLength: number = (someValue as string).length;
在jsx里只能使用as语法
readonly修饰符
表示属性只读，无法被赋值并且无法赋给其他变量：
let a: number[] = [1, 2, 3, 4];
let ro: ReadonlyArray<number> = a;
ro[0] = 12; // error!
ro.push(5); // error!
ro.length = 100; // error!
a = ro; // error!
可以利用断言重新赋值：
a = ro as number[];
类的readonly属性，只能在声明时或者构造函数里被初始化
class Octopus {
readonly name: string;
readonly numberOfLegs: number = 8;
constructor (theName: string) {
this.name = theName;
}
}
let dad = new Octopus("Man with the 8 strong legs");
dad.name = "Man with the 3-piece suit"; // 错误! name 是只读的.
protected修饰符
protected成员在派生类中仍然可以访问。
构造函数也可以被标记成 protected。 这意味着这个类不能在包含它的类外被实例化，但是能被继承。比如
// Employee 能够继承 Person
class Employee extends Person {
private department: string;
constructor(name: string, department: string) {
super(name);
this.department = department;
}
public getElevatorPitch() {
return `Hello, my name is ${this.name} and I work in ${this.department}.`;
}
}
let howard = new Employee("Howard", "Sales");
let john = new Person("John"); // 错误: 'Person' 的构造函数是被保护的.
枚举
枚举类型与数字类型兼容，并且数字类型与枚举类型兼容。不同枚举类型之间是不兼容的。比如，
enum Status { Ready, Waiting };
enum Color { Red, Blue, Green };
let status = Status.Ready;
status = Color.Green; // Error
