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)