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]);

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.

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]));

Answer 3

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 4

Use

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

Answer 5

[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))