Typescript 实现函数重载的方式
作者：你也向往长安城吗
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,本文给大家介绍了Typescript 实现函数重载的方式,需要的朋友可以参考下
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<string, Function> = 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<"number" | "string" | "boolean" | "function" | "object" | "symbol" | "undefined" | "bigint">, 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<string, Function>();
protected addImpl ( name: string, args: Array<"string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function">, 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" );
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