isUndefined always returns false

[Michiel Helvensteijn]

Hi, Thanks for a useful library!

There's a problem with 'lodash-bound/isUndefined'. It always returns false. Other similar functions, like 'isNumber' work fine:

https://tonicdev.com/579e050049cba51300e9aedd/579e050049cba51300e9aede

I'm not sure why. I guess undefined is a special case.

[Elad Ossadon]

Good point. Apparently fn.call(undefined) doesn't pass undefined as an argument, and this remains global (or window in a browser).

http://jsbin.com/fimahal/edit?js,console

function f() {
  console.log(Object.prototype.toString.call(this))
  return this
}

const call1 = f.call(1)
console.log(call1 == 1)

const callUndefined = f.call(undefined)
if (callUndefined === window) {
  console.log('fail - callUndefined returned window')
}
else if (callUndefined === undefined) {
  console.log('success - callUndefined returned undefined')
}

Tricky one. I could compare this to global and if so, to use undefined, but what happens if global is intentionally sent to a method?

Another thing I just found out is that the JS engine wraps primitives. 1 becomes new Number(1) when accessing this. So === comparison returns false.

Keeping this open until I find or suggested a better solution. I'm leaning towards treating global as undefined. But it's definitely a gotcha.

[Michiel Helvensteijn]

It's a tricky choice, indeed. People might well try global::isUndefined() to test whether they're in a browser.

I would propose that, if someone imports lodash-bound/isUndefined, you print an error to the console to explain the situation. Also provide two working versions: lodash-bound/isUndefined-no-error-node and lodash-bound/isUndefined-no-error-browser, and make both behave accordingly.

As for primitives being wrapped in an object, good point. Some of the other methods will misbehave too, like isObject:

https://tonicdev.com/579e050049cba51300e9aedd/57a0ae8d79342e13001cc6b6

For those, I'd propose a similar solution. If they are imported directly, print a warning to the console. Also provide a clean version lodash-bound/isObject-no-warning that doesn't print the warning. Importing that specific file indicates that the developer is aware of the limitations.

All of this in addition to good documentation, of course.

[John-David Dalton]

Use the "use strict" directive in lodash-bound/scripts/method.ejs to allow a this binding of undefined.
Our _.isNumber method works for number primitives and objects.

[Michiel Helvensteijn]

@jdalton Nice, an actual real solution!

And strict mode solves the other problem too. Binding a primitive value won't wrap it in an object. :-)

So this should be a very simple fix.

[Elad Ossadon]

Yep, on it! Thanks @jdalton and @mhelvens for reporting.

[Elad Ossadon]

Releases 1.1.2.