原生js实现on和emit

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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;             //设长度为0比obj[name] = []更优，因为如果是空数组则又开辟了一个新空间，设长度为0则不必开辟新空间         }      } }   export default {     $on,     $emit,     $off }

　

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转载自：http://www.cnblogs.com/aisiqi-love/p/10594461.html