6.2 使用对象

//创建对象
let myData = new Object(); 
//对象赋值
myData.name = "Adam";
myData.weather = "sunny";

6.2.1 使用对象字面量

let myData = {
    name: "Adam",
    weather: "sunny"
}

对于要定义的属性用:号隔开，用,号分隔不同属性。

6.2.2 将函数用作方法

let myData = {
    name: "Adam",
    weather: "sunny",
    printMessage: function () {
        console.log("Hello "+ this.name +". ");
        console.log("Today is  "+ this.weather +". ");
    }
}

myData.printMessage();

注意：方法中引用对象定义的属性，必须使用this关键字

6.2.3 定义类

class关键字用于声明一个类,其后是类名。

class MyClass {

    constructor (name,weather){
        this.name = name;
        this.weather = weather;
    }

    printMessage(){
        console.log("Hello "+ this.name +". ");
        console.log("Today is  "+ this.weather +". ");
    }

}

定义类的设置器和读取器属性

    constructor (name,weather){
        this.name = name;
        this._weather = weather;
    }

set weather( value ){
    this._weather = value;
}

get weather(){
    return `Today is ${weather}`;
}

读取器和设置器实现方式：在函数名称前面加上get或set关键字

JavaScript类中没有访问控制的概念，约定内部属性的名称统一使用下划线(符号_)作为前缀。

使用类继承

extends关键字用于声明将要继承的类（被称为超类或者基类）

super关键字用于调用超类的构造函数或方法

class MySubClass extends MyClass{

    constructor (name ,weather, city){
        super(name,weather);
        this.city = city;
    }

    printMessage(){
        super.printMessage();
        console.log(`You are in ${city}`);
    }

}

let myData = new MySubClass("Adam","sunny","London");
myData.printMessage();

6.3 处理JavaScript模块

创建和使用模块

默认情况：JavaScript和Typescript文件中定义的类、函数和变量就只能在该文件中访问。

export关键字用于在文件之外访问特性。

import关键字用于声明对模块所提供特性的依赖关系。

创建一个名为NameAndWeather.ts文件内容

export class Name {

    constructor(first,second){
        this.first = first;
        this.second = second;
    }

    get nameMessage(){
        return `Hello ${this.first}  ${this.second}`;
    }
}

export class WeatherLocation{

    constructor(weather,city){
        this.weather = weather;
        this.city = city;
    }

    get weatherMessage(){
        return `It is ${weather} in ${this.city}`;
    }
}
import {Name,WeatherLocation} from './module/NameAndWeather';
重命名导入
export class Name {
    get message{
        return 'Other Name';
    }
}

import {Name as OtherName} from './module/xxx';
导入模块中所以类型
import * as NameAndWeatherLocation from './module/NameAndWeather';

let name = new NameAndWeatherLocation.Name("Adam","Freeman");
let loc  = new NameAndWeatherLocation.WeatherLocation("raining","London");

6.4 有用的Typescript特性

为属性和变量添加类型注解

export class Name {

    first: string;
    second: string;

    constructor(first: string ,second: string ){
        this.first = first;
        this.second = second;
    }

    get nameMessage() : string {
        return `Hello ${this.first}  ${this.second}`;
    }
}

export class WeatherLocation{

    constructor(weather: string,city: string){
        this.weather = weather;
        this.city = city;
    }

    get weatherMessage(): string{
        return `It is ${weather} in ${this.city}`;
    }
}

指定多个类型或任意类型

Typescript允许指定多个类型，使用字符|进行分隔。

export class TempConverter {

    static convertFtoC(temp: number | string){
        let value: number = (<number> temp).toPrecision ? <number> temp : parseFloat(<string> temp);
        return xxx;//代码忽略，此处不做实现
    }
}

使用<>字符表示声明一个类型断言，尝试将一个对象转换为指定的类型。还可以使用as关键字达到同样效果。

export class TempConverter {

    static convertFtoC(temp: number | string){
        let value: number = (temp as number).toPrecision ? temp as number : parseFloat(<string> temp);
        return xxx;//代码忽略，此处不做实现
    }
}

使用元组

元组：固定长度的数组，数组的每一项都是指定的类型。

let tuple: [string,string,string];

tuple = ["London","raining","38"];

使用可索引的类型

let cities: {[index:string]: [string,string]} = {};

cities["London"]=["raining","38"];

键：字符串

数据值：元组

只有number和string值可以用作可索引类型的键。