FormData.get function is undefined
By default, Chrome does not support the .get() method, as well as delete, get, getAll, has, and set. Although you can enable that functionality by activating an experimental flag, note from MDN:
[2] Chrome support for methods other than append is currently behind the "Enable Experimental Web Platform Features" flag.
For activating flags in Chrome you can go to the following link:
chrome://flags/#enable-experimental-webkit-features
The answer is this: FormData appeared long ago, but not everyone has updated the software ... so Chrome 49.0 pops up somewhere ... or some mobile browsers.
Solution: use other methods of collecting and submitting the form like jquery or https://stackoverflow.com/a/11661219/12972080.