数据处理之扁平化

            var arr = [1,2,[[[['p',123,[[{},[null]]]]]]],5,[1,[6,[0,[[[null]]]]]],6,3];
            
            function isArray (arr) {
                return Object.prototype.toString.call(arr) == "[object Array]"
            }
            
            function flatten (arr) {
                var arr = arr || [],
                    len = arr.length,
                    resArr = [];
                for(var i = 0; i < len; i++) {
                    if (isArray(arr[i])) {
                        resArr = resArr.concat(flatten(arr[i]))
                    } else{
                        resArr.push(arr[i])
                    }
                }
                return resArr 
            }

数组原型上定义

            
            Array.prototype.flatten = function () {
                var resArr = [];
                this.forEach(function (item) {
                    Object.prototype.toString.call(item) == "[object Array]" ? resArr = resArr.concat(item.flatten()) : resArr.push(item);
                })
                
                return resArr;
            }

用reduce

            Array.prototype.flatten2 = function () {
                return this.reduce(function (prev,next) {
                    return Object.prototype.toString.call(next) == "[object Array]" ? prev.concat(next.flatten2()) : prev.concat([next])
                },[])
            }
            
            
            function flatten2 (arr) {
                var arr = arr || [];
                return arr.reduce(function (prev,next) {
                    return Object.prototype.toString.call(next) == "[object Array]" ? prev.concat(flatten2(next)) : prev.concat([next])
                },[])
            }

上面要注意, 不能用prev.push(next) 代替 prev.concat([next])
原因是 prev.push(next) 语句执行后的返回值是 next 将会赋值给prev

es6简化

            const flatten3 = (arr=[]) => arr.reduce((prev,next) => Object.prototype.toString.call(next) == "[object Array]" ? prev.concat(flatten3(next)) : prev.concat([next]),[])