javascript - 递归地展平数组

Question

我尝试递归地实现数组展平函数。这是代码:

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


console.log(flatten([1, 2, 3, 4, [5]]));
/*
result: [1, 2, 3, 4]
expected: [1, 2, 3, 4, 5]
*/

但是不知道为什么结果不对。请帮我解释一下。

Answer 1

The concat() method returns a new array comprised of the array on which it is called joined with the array(s) and/or value(s) provided as arguments.

flatArr.concat(...) 不会改变 flatArr...你需要像这样分配它:

flatArr = flatArr.concat('flatten(arr[i]));

这是一个具有 3 层深度数组的工作示例:

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

var arr = [1,2,3,4,[5,6,[7,8]]];
var flatten = flatten(arr);

$('#result').html(JSON.stringify(flatten));

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="result"></div>

您可以阅读更多关于 Array.concat function 的信息这里