The boolean "good" casting could be better

[airbnb]

The boolean "good" casting could be better

[ssorallen]

The example uses a Number, but the Boolean casting section is intended to be generic for any type. !!variable will cast any JavaScript type to a Boolean type.

What if age === 0 is a valid state? hasAge would be false in your example, but !!age would be true.

I agree checking values of Numbers should be done differently, but checking for truthiness is straightforward with !!.

Actually you completely missed the point. First of all if age === 0 is a
valid state you would write age >= 0, not age === 0. The actual point is
there is no conversation between any type and bool. Types are not
convertible to truth. All types are truth. Only conditions are true or
false. And further the point is about readability and expressiveness and
maintainability. But elaborating on this any further won't help, if you
don't get it from my original post you can stick with your style, I only
wanted give you some of what I know.

On Fri, Nov 8, 2013 at 4:16 AM, Ross Allen [email protected] wrote:

The example uses a Number, but the Boolean casting section is intended to
be generic for any type. !!variable will cast any JavaScript type to a
Boolean type.

What if age === 0 is a valid state? hasAge would be false in your
example, but !!age would be true.

I agree checking values of Numbers should be done differently, but
checking for truthiness is straightforward with !!.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/97#issuecomment-28027076
.

[ssorallen]

The Boolean section is a possibly-too-abbreviated check for existence. What do you think of:

var hasAge = (age != null);

I can see how the double bang could be misinterpreted or possibly lead to the wrong value.

[serbanghita]

I agree with @bobef on " Only conditions are true or false. And further the point is about readability and expressiveness and maintainability."

Maybe the context is important, still var age = isNaN; !!age; is true and it gets confusing ... I prefer to avoid !! approach.

[jaseemabid]

+1 to avoid !!.
!!"" being false is also error prone. An empty string is not the same as having no string at all.

[goatslacker]

Pruning this one. Feel free to reopen if you feel strongly about it.

[ut3saturn]

Superb. Can you tell if casting is being used here? Or does this == operator have its vulnerabilities as well?

console.log(23 == "23")

Hard to tell if casting happens to the left side in order to compare it with the right. Would a true value occur?

[ljharb]

@ut3saturn I’m not sure what you’re asking, exactly - all == operations do type conversions. As for which side is coerced, the rules are consistent but hard to understand, which is why it’s better to make the coercion explicit and use ===.

[sstern6]

I was wondering what airbnb style guides thinks about the !!.

Is there a rule pref for/against:

const arr = [1,2,3];

if (!!arr.length) {
  // do something
}

To ensure the that the check for arr.length is a boolean value not a truthy or falsey value?

[ljharb]

@sstern6 !!x is ideal to coerce to a boolean; but https://github.com/airbnb/javascript#comparison--shortcuts already discusses that you shouldn't rely on 0 being falsy; that for "length", you should always explicitly compare to a number.