接口使用的几种表现形式：

一、可选属性，只读属性;

interface SquareConfig {
  color?: string;  //可选属性
  width?: number;  //可选属性
  readonly x: number; //只读属性
  readonly y: number;  //只读属性
}

function createSquare(config: SquareConfig): {color: string; area: number} {
  let newSquare = {color: "white", area: 100};
  if (config.color) {
    newSquare.color = config.color;
  }
  if (config.width) {
    newSquare.area = config.width * config.width;
  }
  return newSquare;
}

let mySquare = createSquare({color: "black"});

二、函数类型

interface SearchFunc {
  (source: string, subString: string): boolean;
}
let mySearch: SearchFunc;
mySearch = function(source: string, subString: string) {
  let result = source.search(subString);
  if (result == -1) {
    return false;
  }
  else {
    return true;
  }
}

三、可索引的类型

interface StringArray {
  [index: number]: string;
}

let myArray: StringArray;
myArray = ["Bob", "Fred"];

let myStr: string = myArray[0];

四、接口继承

interface ClockInterface {
    currentTime: Date;
    setTime(d: Date);
}

class Clock implements ClockInterface {
    currentTime: Date;
    setTime(d: Date) {
        this.currentTime = d;
    }
    constructor(h: number, m: number) { }
}

五、扩展接口

interface Shape {
    color: string;
}

interface PenStroke {
    penWidth: number;
}

interface Square extends Shape, PenStroke {
    sideLength: number;
}

let square = <Square>{};
square.color = "blue";
square.sideLength = 10;
square.penWidth = 5.0;

五、接口继承类

class Control {
    private state: any;
}

interface SelectableControl extends Control {
    select(): void;
}

class Button extends Control {
    select() { }
}
class TextBox extends Control {
    select() { }
}
class Image {
    select() { }
}
class Location {
    select() { }
}