Solutions using value.toUpperCase seem to have the problem that typing text into the field resets the cursor position to the end of the text. Solutions using text-transform seem to have the problem that the text submitted to the server is still potentially lowercase. This solution avoids those problems:
function handleInput(e) {
var ss = e.target.selectionStart;
var se = e.target.selectionEnd;
e.target.value = e.target.value.toUpperCase();
e.target.selectionStart = ss;
e.target.selectionEnd = se;
}