Question: x == null rule

[rstacruz]

The readme says:

Always use === instead of == – but obj == null is allowed to check null || undefined.

Why is == being permitted in this exception?

[dcousens]

Probably because it broke a lot a lot of peoples code/assumptions otherwise.

[rstacruz]

in that case, perhaps it should be considered for deprecation?

[dcousens]

Possibly, there might be more to it. @feross?

[feross]

It's a very common idiom in JS to check for null and undefined in one shot by using == null.

x == null is far nicer than x === null || x === undefined to the trained eye.

[dcousens]

IMHO, if they can afford to be that loose with their arguments, I'd prefer just if (!x) {.
If they need to be specific enough such that == null is an option, IMHO they should be doing === null || === undefined.
But, that is just my opinion.

[feross]

!x catches a bunch of other things like the empty string and the number 0. The == null idiom is common in node.js core and on npm.

@dcousens Maybe you're right, but this ship has sailed and it's not worth a breaking change.

[dcousens]

@feross not even in a 6.0.0 if/when that happens?