uppercase form textfield
However if there is a simple(er) solution I prefer that.  


Sorry, maybe I going too deep, but the most simpler solution that you can use just for display is a CSS solution.

Based in your example:

input[name='elementName'] {
  text-transform: uppercase;
}


That's it, any char will be uppercase in your textfield. If need store in uppercase, just change case before save.