Filter null from an array in JavaScript

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.

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]));

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