Question

I do not seem to find what version of a “onkeyup” is correct:

camelcase: onKeyUp

or

lowercase: onkeyup

[UPDATE] http://www.w3.org/TR/html4/intro/sgmltut.html mentions:

“Attribute names are always case-insensitive.”

Answer 1

HTML isn’t case sensitive. So either are fine if they are in the HTML element, like so:

<div onkeyup='alert()'></div>

However, JavaScript is case sensitive. Only lower case will work there:

document.getElementById('div').addEventListener('keyup', function (){
    someCode();
}, false);