函数重载
JavaScript并没有提供函数重载
TypeScript提供的函数重载,仅仅用作提示效果,实现还需手动
函数重载简单点说就是,同一个函数的不同实现方式,根据传入的参数的类型或者长度,决定最终调用哪一个实现
最终效果,TypeScript的类型校验也会变化
code
创建函数重载函数
根据参数的类型,调用不同的实现,如果没有对应的实现,则报错。
export function createOverload () { const map: Map = new Map(); const overload = ( ...args: any[] ) => { const key = args.map( it => typeof it ).join( " " ); const fn = map.get( key ); if ( !fn ) throw new Error( "No overload function matched" ); return fn( args ); }; overload.addImpl = function ( args: Array, fn: Function ) { if ( typeof fn !== "function" ) throw new Error( "last argument must be a function" ); const key = args.join( " " ); map.set( key, fn ); }; return overload; }
使用
const overload = createOverload() overload.addImpl(["string","number"],()=>{ console.log("string number") }) overload.addImpl(["number","string"],()=>{ console.log("number string") }) overload("yang jun",18) // console.log("string number") overload(18,"yang jun") // console.log("number string")
封装一层,因为上述使用没有代码提示,离了代码提示活不下去了
创建抽象类。
在JS中创建抽象类方法,在construct中执行 if( new.target === Overload ) throw new Error("不允许直接new")
在下述实现中,转为 es6 类实现,新增了重载函数的映射表,用于继承类的多个函数的重载。
export abstract class Overload { private overloads = new Map(); protected addImpl ( name: string, args: Array, fn: Function ) { let overload = null; if ( this.overloads.has( name ) ) { overload = this.overloads.get( name ); } else { overload = createOverload(); this.overloads.set( name, overload ); } overload.addImpl( args, fn ); }; protected getOverload ( name: string ): Function | undefined { if ( this.overloads.has( name ) ) return this.overloads.get( name ); throw new Error( "No overload matched" ); } }
使用
非常舒服,再也不用自己在函数中写一串的 if 了
import { Overload } from "./utils"; class Test extends Overload { constructor () { super(); this.addImpl( "getInfo", [ "boolean", "number", "string" ], () => { console.log( "boolean", "number", "string" ); } ); this.addImpl( "getInfo", [ "number", "string", "boolean" ], () => { console.log( "number", "string", "boolean" ); } ); this.addImpl( "getInfo", [ "string", "number", "boolean" ], () => { console.log( "string", "number", "boolean" ); } ); } getInfo ( age: number, name: string, isHandsome: boolean ): Object; getInfo ( isHandsome: boolean, age: number, name: string ): Object; getInfo ( name: string, age: number, isHandsome: boolean ): Object; getInfo (): Object { const overload = this.getOverload( "getInfo" ); return overload( ...arguments ); } getName ( name: string ) { } } const test = new Test(); test.getInfo( 18, "yang jun", true ); // console.log( "number", "string", "boolean" ); test.getInfo( "yang jun", 18, true ); // console.log( "string", "number", "boolean" ); test.getInfo( true, 18, "yang jun" ); // console.log( "boolean", "number", "string" );
以上就是Typescript 实现函数重载的方式的详细内容,更多关于Typescript函数重载的资料请关注IT俱乐部其它相关文章!