原生js實現on和emit

let obj = {};
const $on = (name,fn)=>{
    if(!obj[name]){
        obj[name] = [];
    }
    obj[name].push(fn);
}

const $emit = (name,val)=>{
    if(obj[name]){
        obj[name].map((fn)=>{
            fn(val);
        });
    }
}

const $off = (name,fn)=>{
    if(obj[name]){
        if(fn){
            let index = obj[name].indexOf(fn);
            if(index > -1){
                obj[name].splice(index,1);
            }           
        }else{
            obj[name].length = 0;
            //設長度爲0比obj[name] = []更優，由於若是是空數組則又開闢了一個新空間，設長度爲0則沒必要開闢新空間
        }  
    }
}

export default {
    $on,
    $emit,
    $off
}

　

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轉載自：http://www.cnblogs.com/aisiqi-love/p/10594461.html