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]);

• user1106925: You should be aware that .filter() does not remove anything from the Array. It creates a new array with the items removed.
• Kowser: Possible duplicate of How to filter() out NaN, null, 0, false in an array (JS)

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:

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

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

• user1106925: 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: 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: @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: 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: Javascript comparison table is quite handy when it comes to testing boolean equivalences.

Answer 2

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]));

• gshaineala: Thanks for the info. On the platform where i learn is doesnt filter null...yet in a debugger it doest filter NaN.
• Henke: There is no problem with NaN in this case.

Answer 3

[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))

Answer 4

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]));

Answer 5

Use

function bouncer(arr) {
 return arr.filter(function(item){
 return !!item;
 });
}
console.log(bouncer([1,"", null, NaN, 2, undefined,4,5,6]));