如何在数组(JS)中过滤()出NaN，null，0，false

问题描述

我被要求在 array 中过滤掉 NaN, null, 0, false.

I was asked to filter out NaN, null, 0, false in an array.

幸运的是我已经回答了这个问题.

Luckily I have answered the question.

function bouncer(arr) {
  function filterer(arr) {
     return arr > 0|| isNaN(arr) === true;
  }
  arr = arr.filter(filterer);
  return arr;
}

//example input
bouncer([0, 1, 2, 3, 'ate', '', false]); //output [1, 2, 3, 'ate']

但问题是我真的不知道我是如何得出答案的，或者更确切地说我不知道它是如何工作的.特别是在 arr > 0 上，过滤器是如何知道 arr 已经在 arr[1]、arr[2] 等上读取的.而不使用循环遍历所有数组.

but the thing is I really don't know how I came up with the answer or rather I don't know how it works. Specially on arr > 0 how did the filter know that arr is alread on arr[1], arr[2], etc.. without using a loop to iterate in all array.

或者可以简单地解释一下代码是如何工作的.[我已经尽力解释清楚了---]

or can simply just explain on how to code works. [I've tried to explain it clearly ---]

推荐答案

查看docs 用于 Array.filter.特别注意回调的参数:

Look at the docs for Array.filter. Notice in particular the arguments to the callback:

测试数组中每个元素的函数.使用参数(元素、索引、数组)调用.返回 true 保留元素，否则返回 false.

Function to test each element of the array. Invoked with arguments (element, index, array). Return true to keep the element, false otherwise.

所以在您的情况下， arr 是元素(并且命名不佳，因此您感到困惑).过滤器循环遍历您的数组，并且对于它调用的每个项目，您都将当前位置的元素作为 arr 进行回调.

So in your case arr is the element (and poorly named, hence your confusion). Filter loops through your array and for every item it calls you callback passing in the element at the current position as arr.

正如其他人在评论中指出的那样，您的过滤器回调的逻辑实际上对于负值是有缺陷的，但是如果您知道您的数组永远不会包含负值(但这可能是危险的)，这可能不是问题假设).

As others have pointed out in the comments, the logic of your filter callback is actually flawed for negative values, but that may not be an issue if you know that your array will never contain negative values (but that can be a dangerous thing to assume).

当然，在内部，这是循环遍历您的数组.如果不触及数组中的每个元素，就无法过滤(未排序的)数组.查看链接中的 polyfil 以了解它可能是如何工作的(可能是因为这是一个实现细节，可能因不同的 javascript 引擎而异，但无疑会在某处涉及循环)，它循环遍历您的数组，调用回调(注意参数)，如果回调返回 true，则将其推送到结果数组中.

And, of course, internally, this is looping through your array. You can't filter your (unsorted) array without touching each element in the array. Look at the polyfil in the link to get an idea of how it might work (might because this is an implementation detail that may differ with different javascript engines, but will no doubt involve a loop somewhere), it loops through your array, calls the callback (note the arguments) and if the callback returns true, it gets pushed onto a results array.

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