TypeScript接口

作者:追风剑情 发布于:2022-4-29 11:42 分类:TypeScript

TypeScript 接口

接口是一系列抽象方法的声明,是一些方法特征的集合,这些方法都应该是抽象的,需要由具体的类去实现,然后第三方就可以通过这组抽象方法调用,让具体的类执行具体的方法。

TypeScript 接口定义如下:

interface interface_name { 
}

实例

以下实例中,我们定义了一个接口 IPerson,接着定义了一个变量 customer,它的类型是 IPerson。

customer 实现了接口 IPerson 的属性和方法。

TypeScript
interface IPerson { 
    firstName:string, 
    lastName:string, 
    sayHi: ()=>string 
} 
 
var customer:IPerson = { 
    firstName:"Tom",
    lastName:"Hanks", 
    sayHi: ():string =>{return "Hi there"} 
} 
 
console.log("Customer 对象 ") 
console.log(customer.firstName) 
console.log(customer.lastName) 
console.log(customer.sayHi())  
 
var employee:IPerson = { 
    firstName:"Jim",
    lastName:"Blakes", 
    sayHi: ():string =>{return "Hello!!!"} 
} 
 
console.log("Employee  对象 ") 
console.log(employee.firstName) 
console.log(employee.lastName)

注意   接口不能转换为 JavaScript。 它只是 TypeScript 的一部分。

编译以上代码,得到以下 JavaScript 代码:

JavaScript
var customer = {
    firstName: "Tom",
    lastName: "Hanks",
    sayHi: function () { return "Hi there"; }
};
console.log("Customer 对象 ");
console.log(customer.firstName);
console.log(customer.lastName);
console.log(customer.sayHi());
var employee = {
    firstName: "Jim",
    lastName: "Blakes",
    sayHi: function () { return "Hello!!!"; }
};
console.log("Employee  对象 ");
console.log(employee.firstName);
console.log(employee.lastName);
输出结果为:
Customer 对象
Tom
Hanks
Hi there
Employee  对象
Jim
Blakes

联合类型和接口

以下实例演示了如何在接口中使用联合类型:

TypeScript
interface RunOptions { 
    program:string; 
    commandline:string[]|string|(()=>string); 
} 
 
// commandline 是字符串
var options:RunOptions = {program:"test1",commandline:"Hello"}; 
console.log(options.commandline)  
 
// commandline 是字符串数组
options = {program:"test1",commandline:["Hello","World"]}; 
console.log(options.commandline[0]); 
console.log(options.commandline[1]);  
 
// commandline 是一个函数表达式
options = {program:"test1",commandline:()=>{return "**Hello World**";}}; 
 
var fn:any = options.commandline; 
console.log(fn());

编译以上代码,得到以下 JavaScript 代码:

JavaScript
// commandline 是字符串
var options = { program: "test1", commandline: "Hello" };
console.log(options.commandline);
// commandline 是字符串数组
options = { program: "test1", commandline: ["Hello", "World"] };
console.log(options.commandline[0]);
console.log(options.commandline[1]);
// commandline 是一个函数表达式
options = { program: "test1", commandline: function () { return "**Hello World**"; } };
var fn = options.commandline;
console.log(fn());
输出结果为:
Hello
Hello
World
**Hello World**

接口和数组

接口中我们可以将数组的索引值和元素设置为不同类型,索引值可以是数字或字符串。

设置元素为字符串类型:

实例
interface namelist { 
   [index:number]:string 
} 
 
// 类型一致,正确
var list2:namelist = ["Google","Runoob","Taobao"]
// 错误元素 1 不是 string 类型
// var list2:namelist = ["Runoob",1,"Taobao"]

如果使用了其他类型会报错:

实例
interface namelist { 
   [index:number]:string 
} 
 
// 类型一致,正确
var list2:namelist = ["Google","Runoob","Taobao"]
// 错误元素 1 不是 string 类型
var list2:namelist = ["Runoob",1,"Taobao"]

执行后报错如下,显示类型不一致:

test.ts:8:30 - error TS2322: Type 'number' is not assignable to type 'string'.

8 var list2:namelist = ["John",1,"Bran"]
                               ~

  test.ts:2:4
    2    [index:number]:string
         ~~~~~~~~~~~~~~~~~~~~~
    The expected type comes from this index signature.


Found 1 error.

TypeScript
interface ages { 
   [index:string]:number 
} 
 
var agelist:ages; 
// 类型正确
agelist["runoob"] = 15  
 
// 类型错误,输出  error TS2322: Type '"google"' is not assignable to type 'number'.
// agelist[2] = "google"

接口继承

○ 接口继承就是说接口可以通过其他接口来扩展自己。
○ Typescript 允许接口继承多个接口。
○ 继承使用关键字 extends

单接口继承语法格式:

Child_interface_name extends super_interface_name

多接口继承语法格式:

Child_interface_name extends super_interface1_name, super_interface2_name,…,super_interfaceN_name

继承的各个接口使用逗号 , 分隔。

单继承实例

TypeScript
interface Person { 
   age:number 
} 
 
interface Musician extends Person { 
   instrument:string 
} 
 
var drummer = <Musician>{}; 
drummer.age = 27 
drummer.instrument = "Drums" 
console.log("年龄:  "+drummer.age)
console.log("喜欢的乐器:  "+drummer.instrument)

编译以上代码,得到以下 JavaScript 代码:

JavaScript
var drummer = {};
drummer.age = 27;
drummer.instrument = "Drums";
console.log("年龄:  " + drummer.age);
console.log("喜欢的乐器:  " + drummer.instrument);

多继承实例

TypeScript
interface IParent1 { 
    v1:number 
} 
 
interface IParent2 { 
    v2:number 
} 
 
interface Child extends IParent1, IParent2 { } 
var Iobj:Child = { v1:12, v2:23} 
console.log("value 1: "+Iobj.v1+" value 2: "+Iobj.v2)

编译以上代码,得到以下 JavaScript 代码:

JavaScript
var Iobj = { v1: 12, v2: 23 };
console.log("value 1: " + Iobj.v1 + " value 2: " + Iobj.v2);

标签: TypeScript

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