checking for null in javascript

Question

if (valid === null) {
  return '';
} else if (!valid) {
  return 'is-not-valid';
} else if (valid) {
  return 'is-valid';
} else {
  return '';
}

I have the above if-else-if chain in the code, trying to see if I can write the same logic in one or two lines.

The else statement will never be hit so you can remove that already. — Felix Kling
– Felix Kling, Commented Nov 24, 2020 at 0:10
why not simply !!valid or Boolean(valid) ? developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Mister Jojo
– Mister Jojo, Commented Nov 24, 2020 at 0:19

Felix Kling · Accepted Answer · 2020-11-24 00:12:15Z

3

Since you want to distinguish between three types of values, you have to make at least two checks already. The else case will never be hit since either !valid or valid will be true. That also means you can reduce the last else if to an else:

if (valid === null) {
  return '';
} else if (!valid) {
  return 'is-not-valid';
} else {
  return 'is-valid';
}

But you could condense this logic using the conditional operator:

return valid === null ? '' : (valid ? 'is-valid' : 'is-not-valid');

answered Nov 24, 2020 at 0:12

Felix Kling

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Comments

Rubydesic · Accepted Answer · 2020-11-24 00:12:24Z

1

Although I think your example (sans the redundant else block) looks pretty good, you can write it on one line like this:

return valid === null ? '' : (valid ? 'is-valid' : 'is-not-valid')

I prefer the original though

answered Nov 24, 2020 at 0:12

Rubydesic

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