ts的函数类型

ts的函数类型

1、函数声明

function sum(x: number,y:number):number {return x+y;}

注意：输入多余（或者少于要求的）参数。是不被允许的：

function sum(x:number,y:number):number {return x + y;}sum(1,2,3);//不被允许

function sum(x:number,y:number):number {return x + y;}sum(1);//不被允许

2、函数表达式

let mySum:(x:number,y:number) =>number = function(x:number,y:number):number {return x+y;}

3、用接口定义函数的形状

interface SearchFun {(source:string,subString:string):boolean;}let mySearch: SearchFun;mySearch = function(source:string,subString:string) {return source.search(subString) != -1;}

4、可选参数

function buildName(firstName:string,lastName?:string) {if(lastName) {return firstName + '' + lastName} else {return firstName}}let tomcat = buildName('Tom','cat');let tom = buildName('Tom')

需要注意的是：可选参数必须在必需参数后面，换句话说，可选参数后面不允许在出现必须参数了。

5、参数默认值

ts中会将添加了默认值的参数识别为可选参数，此时就不受【可选参数必须接在必需参数后面】的限制了

function buildName(firstName:string = 'Tom',lastName:string) {return firstName + '' + lastName;}let tomcat = buildName('Tom','Cat');let cat = buildName(undefined,'Cat');

6、剩余参数

function push(array:any[],..items:any[]) {items.forEach(function(item) {array.push(item);})}let a = [];push(a,1,2,3);

7、重载

function reverse(x:number):number;function reverse(x:string):string;function reverse(x:number | string):number | string | void {if(typeof x === 'number') {retrun Number(x.toString().split('').reverse().join(''))} else if(typeof x === 'string') {return x.split('').reverse().join('');}}

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