fix checking for FormData existence

[yeonhoyoon]

in Safari, typeof FormData returns "object" instead of "function"

[ded]

In that case, is there a more legit way of checking like seeing if it has any unique properties?

[keronsen]

Isn't o['data'] instanceof FormData enough on its own? Why is the typeof check neccesary?

[yeonhoyoon]

@keronsen In older browsers, FormData is not defined, so o['data'] instanceof FormData will throw ReferenceError.

[thomsbg]

Any updates on this? According to @yeonhoyoon's last comment, perhaps the check should be:

typeof FormData !== 'undefined', or 'FormData' in window