TS Interface

An interface is a declaration of a series of abstract methods , Is a collection of method features .
These methods should be abstract , It needs to be implemented by specific classes , Let specific classes execute specific methods .

1. Simple interface instance

//  Define an interface  User
interface User {
    
	name: string,
   	age: number,
    sing: ()=>string
}

// Define a variable  xiaoXu
let xiaoXu: User = {
    
	name: " Xiao Xu ",
	age: 18,
	sing: ():string => " Xu Qianjin "
}

console.log(xiaoXu.name); // Xiao Xu 
console.log(xiaoXu.age); //18
console.log(xiaoXu.sing()); // Xu Qianjin 

2. Union types and interfaces

interface RunOptions {
     
    program:string; 
    commandline:string[]|string|(()=>string); 
} 
 
// commandline  Is string 
var options:RunOptions = {
    
    program:"test1",
    commandline:"Hello"
}; 
console.log(options.commandline)  
 
// commandline  It's an array of strings 
options = {
    
    program:"test1",
    commandline:["Hello","World"]
}; 
console.log(options.commandline[0]); 
console.log(options.commandline[1]);  
 
// commandline  It's a function expression 
options = {
    
    program:"test1",
    commandline:()=>{
    return "**Hello World**";}
}; 
 
var fn:any = options.commandline; 
console.log(fn());

3. Interfaces and arrays

The index value and element of the array can be set to different types in the interface , The index value can be a number or a string .
Set element to string type ：

interface namelist {
     
   [index:number]:string 
} 
var list1:namelist = ["Google","Runoob","Taobao"]; //  The same type , correct 
var list2:namelist = ["Runoob",1,"Taobao"]; //  Error element  1  No  string  type 

4. Interface inheritance

Interface inheritance means that an interface can extend itself through other interfaces .

TS Allow interfaces to inherit multiple interfaces , Use keywords extends.

4.1 Single interface inheritance

interface Person {
     
   age:number 
} 
 
interface Musician extends Person {
     
   instrument:string 
} 
 
var drummer = <Musician>{
    }; 
drummer.age = 27 
drummer.instrument = "Drums" 
console.log(" Age : "+drummer.age)
console.log(" A favorite musical instrument : "+drummer.instrument)

4.2 Multi interface inheritance

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)