How to filter() out NaN, null, 0, false in an array (JS)

Question

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

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']

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.

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

Answer 1

If you were asked to filter out NaN, null, 0, false in an array, then your solutions doesn't really work.

Your input of:

bouncer([0, 1, 2, 3, 'ate', '', false, NaN]);

Will get the output of:

[1, 2, 3, 'ate', NaN]

To filter out all 'falsy' values you can simply use Boolean:

function bouncer(arr) {
  return arr.filter(Boolean);
}

bouncer([0, 1, 2, 3, 'ate', '', false, NaN]);

Output:

[1, 2, 3, 'ate']

---

Since the Boolean constructor is also a function, it returns either true for ‘truthy’ argument or false for ‘falsy’ argument. If the value is omitted or is 0, -0, null, false, NaN, undefined, or the empty string (""), the object has the value of false. All other values, including any object or the string "false", create an object with an initial value of true.

Answer 2

You can also use an identity function instead of Boolean.

function bouncer(arr) {
  return arr.filter(x => x);
}