Js自定义数组map之bigmap

         /**
          * like map,but prev,curr,next and index will be given
          * @param  {Function} cb Callback,the parameters ara prev,curr,next and index
          * @return {[type]}      [description]
          */
         Array.prototype.bigmap=function(cb){
             var copy = this.slice(0);
             var len = this.length;
             for (var i = 0; i < len; i++) {
                 var curr = this[i];
                 var prev = i==0?undefined:this[i-1];
                 var next = i==len?undefined:this[i+1];
                 var ret = cb(curr,prev,next,i);
                 if(ret){
                     copy[i]=ret;
                 }
             }
             return copy;
         }

         //写个栗子
         // [1,2,3,4,7,9,10,50]  =>  ["1-4", "7", "9-10", "50"]

         var arr = [1,2,3,4,7,9,10,50];
         arr = arr.bigmap(function(curr,prev,next,i){
             // console.log(curr+"--"+prev+"--"+next+"--"+i)
             if(prev+1==curr){
                 var ret = "_";
                 if(next-1!=curr){
                     ret += curr;
                 }
                 return ret;
             }
         }).filter(function(obj){
             return obj!="_";
         }).toString().replace(/,_/g,"-").split(",");

         console.log(arr)