Why won't this code work on a string?

Question

So i am practicing algorithms(javascript), and i come across this challenge, where we have to filter an array, remove the following elements:

false, NaN, undefined, "", null, 0

My code seems to have problems with strings and chars, it failed these tests.

-bouncer([7, "ate", "", false, 9]) should return [7, "ate", 9] (returned [7, 9])

-bouncer(["a", "b", "c"]) should return ["a", "b", "c"] (returned [])

    function bouncer(arr) {
        return arr.filter(function(element)
                {
                    if (element != false && !isNaN(element) && element != null && element != "" && element != undefined)
                        {return element;}
                }
               );
    }

I would love a simple explanation of the concept i am missing

You're falling into the JavaScript coercion problem. See [this question and its answers](https://stackoverflow.com/q/825402/215552) for more on how `isNaN` behaves on strings. — Heretic Monkey, Oct 09 '17 at 17:25

score 1 · Answer 1 · answered Oct 09 '17 at 17:25

1

function bouncer(arr) {
    return arr.filter(function(element) {
            if (element) {
                return element;
            }
        }
    );
}

Here is the answer for you.

answered Oct 09 '17 at 17:25

Gautam

815
6
15

Sure, the problem is !isNaN("ate"); will be false for all string and chars :) – Gautam Oct 09 '17 at 17:34
No need for the `if` condition really. You could pretty much just return the element and it would work. – MinusFour Oct 09 '17 at 17:34

score 0 · Answer 2 · answered Oct 09 '17 at 17:26

0

Beside the given coercion propblem with != instead of !==, you could filter by using Boolean as callback, which returns truthy elements.

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

console.log(bouncer([7, "ate", "", false, 9])); // [7, "ate", 9]
console.log(bouncer(["a", "b", "c"]));          // ["a", "b", "c"]

answered Oct 09 '17 at 17:26

Nina Scholz

376,160
25
347
392

Well this will fail in case of console.log(bouncer([7, "ate", "", false, 9, new Boolean(false)])); – Gautam Oct 09 '17 at 17:28
@Gautam, an object instance is always truthy, despite of their `this` value. – Nina Scholz Oct 09 '17 at 17:29
Oh yes, thnks :) – Gautam Oct 09 '17 at 17:37

score 0 · Answer 3 · answered Oct 09 '17 at 17:39

0

The below code works for all the conditions. Please have a look at it.

function bouncer(arr) {
    return arr.filter(function(element) {
        if (element && element.trim().length > 0 && element != "NaN") {
            return element;
        }
    });
}

answered Oct 09 '17 at 17:39

Shrikant Potty

1

@vishwad - The code shared by Gautam doesn't check for 'NaN', so please keep a check for that as well in your code. Thanks! – Shrikant Potty Oct 09 '17 at 17:40

Why won't this code work on a string?

3 Answers3