Report the actual type when PropTypes.instanceOf fails

[jorrit]

When PropTypes.instanceOf fails, the error text does not report what the type of the actual prop is. This PR adds the type of the actual prop.

[zpao]

How is this not throwing when props[propName] === null?

[zpao]

Oh right, null doesn't actually come into this check because it does the isRequired check first.

[zpao]

If the value is Object.create(null), then we'll throw here. We should guard against that.

[zpao]

Sorry I talked to myself in there… I think this seems reasonable. There could still be some false positives - eg, two different c'tors that both have Cat as their name, or more likely problems with primitives (eg 5 instanceof Number will fail the proptype check but then the message will say that it expected Number and got Number) but that's why we have the other primitive proptype checkers.

[jorrit]

Yes, the nature of Javascript is such that explaining the type checks is hard. In cases that someone has two different classes with the same name it could be the case that 'Cat' is not 'Cat', but someone using class name multiple times should expect something like that, in my opinion.

I'll update the code.

[jorrit]

I have updated the commit of my branch to incorporate the check you recommended.

[zpao]

Thanks!

[jorrit]

Thanks for merging!