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. — user1106925
– user1106925, Commented Dec 27, 2016 at 14:34
Possible duplicate of How to filter() out NaN, null, 0, false in an array (JS) — Kowser
– Kowser, Commented Aug 16, 2017 at 22:27

Henke · Accepted Answer · 2021-03-17 13:10:25Z

129

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, 2021 at 13:10

Henke

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answered Dec 27, 2016 at 14:24

tymeJV

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5 Comments

user1106925 Over a year ago

And you don't need the !!. Just x=>x is enough, though @PranavCBalan's way doesn't require creation of a function. .filter(Boolean)

gshaineala Over a year ago

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.

tymeJV Over a year ago

@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.

gshaineala Over a year ago

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.

Stphane Over a year ago

Javascript comparison table is quite handy when it comes to testing boolean equivalences.

Nina Scholz · Accepted Answer · 2016-12-27 14:41:10Z

36

It is a problem with NaN, because

NaN !== NaN

2 Comments

gshaineala Over a year ago

Thanks for the info. On the platform where i learn is doesnt filter null...yet in a debugger it doest filter NaN.

Henke Over a year ago

There is no problem with NaN in this case.

Hari Kishore · Accepted Answer · 2022-08-22 08:59:39Z

10

[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, 2022 at 8:59

answered Oct 23, 2021 at 10:12

Hari Kishore

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Comments

kukkuz · Accepted Answer · 2016-12-27 14:26:10Z

7

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, 2016 at 14:26

kukkuz

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Comments

Jyothi Babu Araja · Accepted Answer · 2016-12-27 14:25:14Z

3

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, 2016 at 14:25

Jyothi Babu Araja

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