Filter null from an array in JavaScript

Question

I have a task to remove false, null, 0, "", undefined, and NaN elements from an given array. I worked on a solution which removes all except null. Anyone can explain why? Here's the code:

function bouncer(arr) {
var notAllowed = ["",false,null,0,undefined,NaN];
  for (i = 0; i < arr.length; i++){
      for (j=0; j<notAllowed.length;j++) {
         arr = arr.filter(function(val) {
               return val !== notAllowed[j];
              });
  }
 }
return arr;
}

bouncer([1,"", null, NaN, 2, undefined,4,5,6]);

question from:https://stackoverflow.com/questions/41346902/filter-null-from-an-array-in-javascript

Answer 1

Well, since all of your values are falsy, just do a !! (cast to boolean) check:

[1,"", null, NaN, 2, undefined,4,5,6].filter(x => !!x); //returns [1, 2, 4, 5, 6]

Edit: Apparently the cast isn't needed:

[1,"", null, NaN, 2, undefined,4,5,6].filter(x => x);

And the code above removes null just fine, it's NaN that's the problem. NaN !== NaN as Nina says in her answer.