数组扁平化

[LiuL0703]

将多维数组转化为一维数组（类似_Underscore.js中的_flatten()函数）

var flatten = function(arr) {
    var res = [], idx = 0, val;
    for (var i =  0, length = arr && arr.length; i < length; i++) {
      val = arr[i];
      if (val && val.length >= 0 && Array.isArray(val)) {
        val= flatten(val);
        var j = 0, len = val.length;
        res.length += len;
        while (j < len) {
          res[idx++] = val[j++];
        }
      } else {
        res[idx++] = val;
      }
    }
    return res;
  }

flatten([1, [2], [3, [[4]]]])   //[1,2,3,4]

如果仅是字符串数组 则可用

arr = arr.join(",").split(",")
["1", ["2"], ["3", [["4"]]]].join(",").split(",")         //  ["1", "2", "3", "4"]

递归

function flatten(arr){
    var res = [];
    for(var i=0;i<arr.length;i++){
        if(Array.isArray(arr[i])){
            res = res.concat(flatten(arr[i]));
        }else{
            res.push(arr[i]);
        }
    }
    return res;
}

利用reduce

function flatten(arr){
    return arr.reduce(function(prev,item){
        return prev.concat(Array.isArray(item)?flatten(item):item);
    },[]);
}