JavaScript-递归

递归使用过程中的两个先决条件：
    1. 要递归的条件。
    2. 递归结束的条件。

Eg： 
    var thisArr = function(arr) {
        var new_arr = [];
        for(var i = 0; i < arr.length; i++){
            if(Array.isArray(arr[i])){
                thisArr(arr[i]);
            }else{
                new_arr.push(arr[i]);
            }
        }
    };
        
    function ladding(){
        var arr = [1,2,3,4,5,["a","b","c","d","e",["A","B","C","D","E",["FIRST","SECOND","THIRED","FOURED","FIRED"]]]];
        thisArr(arr);
        console.log(new_arr);
    }