调用函数后如何重置全局变量？

Question

I've written a function with recursive approach to get the values from nested Array. The problem is, I can't reset the global variable after each call. Here after every call the results are being appended to previous result instead of giving new result. I know, Global variable isn't being reset, so data will always append. But I can't define the variable inside the function as its recursive call.

How can I avoid this situation? Any help would be appreciated.

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

getData([1, [2], [3, [[4]]]]); // res = [1, 2, 3, 4]
getData([[["a"]], [["b"]]]);   // res = [1, 2, 3, 4, "a", "b"], expected is res = ["a", "b"];
getData([1, {}, [3, [[4]]]]);

Answer 1

But I can't define the variable inside the function as its recursive call.

You can define the result variable inside the function but you need to properly deal with the return values of your recursive calls:

function getData(arr) {
    var res = [];

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

    return res;
}

(And you don't need to make the result array a parameter of the function.)

Answer 2

Landed up with another solution using closure, it might help someone.

function getData(arr) {
  var res = [];
  return innerGetData(arr);

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

Answer 3

Hey a variant of the solution above is:

 function steamrollArray(arr) { var newArr = []; arr.forEach(function(el){ if(!Array.isArray(el)){ newArr.push(el); } else { newArr = newArr.concat(steamrollArray(el)); } }); return newArr; } 

:)

Answer 4

Use pop(array_name) to remove the last item from the array after you're done with it.

-- Ada