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]);

You should be aware that `.filter()` does not remove anything from the Array. It creates a new array with the items removed. — , Dec 27 '16 at 14:34
Possible duplicate of [How to filter() out NaN, null, 0, false in an array (JS)](https://stackoverflow.com/questions/31925323/how-to-filter-out-nan-null-0-false-in-an-array-js) — Kowser, Aug 16 '17 at 22:27

score 120 · Accepted Answer · edited Mar 17 '21 at 13:10

120

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:

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

And the code above removes "", null, undefined and NaN just fine.

edited Mar 17 '21 at 13:10

Henke

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answered Dec 27 '16 at 14:24

tymeJV

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And you don't need the `!!`. Just `x=>x` is enough, though @PranavCBalan's way doesn't require creation of a function. `.filter(Boolean)` – Dec 27 '16 at 14:29
Yes, your solution works.Thanks for that,but..i'm just starting to learn js so yea..it will help me to understand why my code doesn't work. – gshaineala Dec 27 '16 at 14:38
2

@squint -- Ahh didnt know that about the case, assumed I needed it. Also didnt know about the sweet `Boolean` rather than function creation... always learning, will make the edit. – tymeJV Dec 27 '16 at 14:39
Ok, i got it now. On the freecodecamp platform where I learn it doesnt filter null but if i run the code in the chrome console it does not filter NaN. Thank you all. – gshaineala Dec 27 '16 at 14:50
[Javascript comparison table](https://dorey.github.io/JavaScript-Equality-Table/) is quite handy when it comes to testing boolean equivalences. – Stphane Feb 22 '18 at 11:39

Nina Scholz · Answer 2 · 2016-12-27T14:41:10.767

32

It is a problem with NaN, because

NaN !== NaN

read more here: Testing against NaN.

For filtering the values, you could check for truthyness.

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

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

edited Dec 27 '16 at 14:41

answered Dec 27 '16 at 14:25

Nina Scholz

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Thanks for the info. On the platform where i learn is doesnt filter null...yet in a debugger it doest filter NaN. – gshaineala Dec 27 '16 at 14:46
There is *no* problem with `NaN` in this case. – Henke Mar 17 '21 at 10:26

Hari Kishore · Answer 3 · 2022-08-22T08:59:39.920

7

[1, 2, 0, null, "sdf", ""].filter(a=>a)
// filter non null value; remove 0, null and "" (empty quote)

console.log([1, 2, 0, null, "sdf", ""].filter(a=>a))

edited Aug 22 '22 at 08:59

answered Oct 23 '21 at 10:12

Hari Kishore

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score 6 · Answer 4 · answered Dec 27 '16 at 14:26

6

You can use Array.prototype.filter for truthy value check - see demo below:

function bouncer(array) {
  return array.filter(function(e) {
    return e;
  });
}

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

answered Dec 27 '16 at 14:26

kukkuz

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score 2 · Answer 5 · answered Dec 27 '16 at 14:25

2

Use

function bouncer(arr) {
 return arr.filter(function(item){
   return !!item;
 });
}

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

answered Dec 27 '16 at 14:25

Jyothi Babu Araja

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Filter null from an array in JavaScript

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