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📜  TypeScript-接口

📅  最后修改于: 2020-10-19 03:54:43             🧑  作者: Mango

接口是实体应遵守的语法契约。换句话说，接口定义了任何实体必须遵守的语法。

接口定义属性，方法和事件，它们是接口的成员。接口仅包含成员的声明。定义成员是派生类的责任。它通常有助于提供派生类将遵循的标准结构。

让我们考虑一个对象-

var person = { 
   FirstName:"Tom", 
   LastName:"Hanks", 
   sayHi: ()=>{ return "Hi"} 
};

如果我们考虑对象的签名，则可能是-

{ 
   FirstName:string, 
   LastName:string, 
   sayHi()=>string 
}

要在对象之间重用签名，我们可以将其定义为接口。

声明接口

interface关键字用于声明接口。这是声明接口的语法-

句法

interface interface_name { 
}

示例：接口和对象

interface IPerson { 
   firstName:string, 
   lastName:string, 
   sayHi: ()=>string 
} 

var customer:IPerson = { 
   firstName:"Tom",
   lastName:"Hanks", 
   sayHi: ():string =>{return "Hi there"} 
} 

console.log("Customer Object ") 
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  Object ") 
console.log(employee.firstName);
console.log(employee.lastName);

该示例定义了一个接口。客户对象的类型为IPerson。因此，现在它将绑定到对象上，以定义接口指定的所有属性。

另一个具有以下签名的对象仍被视为IPerson，因为该对象由其大小或签名来对待。

编译时，它将生成以下JavaScript代码。

//Generated by typescript 1.8.10
var customer = { firstName: "Tom", lastName: "Hanks",
   sayHi: function () { return "Hi there"; }
};
console.log("Customer Object ");
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  Object ");
console.log(employee.firstName);
console.log(employee.lastName);

上面的示例代码的输出如下-

Customer object 
Tom 
Hanks 
Hi there 
Employee  object 
Jim  
Blakes 
Hello!!!

接口不得转换为JavaScript。它只是TypeScript的一部分。如果您看到TS Playground工具的屏幕快照，则在声明与类不同的接口时，不会发出Java脚本。因此，接口对运行时JavaScript的影响为零。

接口和对象

联合类型和接口

以下示例显示联合类型和接口的用法-

interface RunOptions { 
   program:string; 
   commandline:string[]|string|(()=>string); 
} 

//commandline as string 
var options:RunOptions = {program:"test1",commandline:"Hello"}; 
console.log(options.commandline)  

//commandline as a string array 
options = {program:"test1",commandline:["Hello","World"]}; 
console.log(options.commandline[0]); 
console.log(options.commandline[1]);  

//commandline as a function expression 
options = {program:"test1",commandline:()=>{return "**Hello World**";}}; 

var fn:any = options.commandline; 
console.log(fn());

编译时，它将生成以下JavaScript代码。

//Generated by typescript 1.8.10
//commandline as string
var options = { program: "test1", commandline: "Hello" };
console.log(options.commandline);

//commandline as a string array
options = { program: "test1", commandline: ["Hello", "World"] };
console.log(options.commandline[0]);
console.log(options.commandline[1]);

//commandline as a function expression
options = { program: "test1", commandline: function () { return "**Hello World**"; } };
var fn = options.commandline;
console.log(fn());

其输出如下-

Hello 
Hello 
World 
**Hello World**

接口和阵列

接口可以定义数组使用的键的类型及其包含的条目的类型。索引可以是字符串类型或数字类型。

例

interface namelist { 
   [index:number]:string 
} 

var list2:namelist = ["John",1,"Bran"] //Error. 1 is not type string  
interface ages { 
   [index:string]:number 
} 

var agelist:ages; 
agelist["John"] = 15   // Ok 
agelist[2] = "nine"   // Error

接口与继承

一个接口可以被其他接口扩展。换句话说，一个接口可以从其他接口继承。 Typescript允许一个接口从多个接口继承。

使用extends关键字在接口之间实现继承。

语法：单接口继承

Child_interface_name extends super_interface_name

语法：多接口继承

Child_interface_name extends super_interface1_name, 
super_interface2_name,…,super_interfaceN_name

示例：简单接口继承

interface Person { 
   age:number 
} 

interface Musician extends Person { 
   instrument:string 
} 

var drummer = {}; 
drummer.age = 27 
drummer.instrument = "Drums" 
console.log("Age:  "+drummer.age) console.log("Instrument:  "+drummer.instrument)

编译时，它将生成以下JavaScript代码。

//Generated by typescript 1.8.10
var drummer = {};
drummer.age = 27;
drummer.instrument = "Drums";
console.log("Age:  " + drummer.age);
console.log("Instrument:  " + drummer.instrument);

其输出如下-

Age: 27 
Instrument: Drums

示例：多接口继承

interface IParent1 { 
   v1:number 
} 

interface IParent2 { 
   v2:number 
} 

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

对象Iobj是接口叶类型。由于继承，接口叶现在具有两个属性-v1和v2。因此，对象Iobj现在必须包含这些属性。

编译时，它将生成以下JavaScript代码。

//Generated by typescript 1.8.10
var Iobj = { v1: 12, v2: 23 };
console.log("value 1: " + this.v1 + " value 2: " + this.v2);

上面代码的输出如下-

value 1: 12   value 2: 23