Today I Learned - Rocky Kev

TIL Casting values to JS booleans

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TAGS: javascript booleans

Sometimes, you get something from a api like:

// json response
{
  type: 'article',
  length: '1200 words',
  publishStatus: 1 // 0 - not published, 1 - published
}

For safety, you really want to cast publishStatus to a boolean.

You can do that with !!.


const isPublished = !!json.publishStatus;

How does it work?

The first bang reverse it and casts it to a boolean. So if it was a falsy value, it'll convert it to true.
The second bang reverses it again to it's original status, but keeping the boolean.

falsy value -> true -> false.

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