jQuery: trigger keypress function on entire document but not inside inputs and textareas?

You’ll have to filter out the elements after the event and not in the selector, like this

$(document).on('keypress', function(e) {
    var tag = e.target.tagName.toLowerCase();
    if ( e.which === 119 && tag != 'input' && tag != 'textarea') 
        doSomething();
});

this checks the tagname of the event.target, the element the event originated from, and only fires the function if the event did not originate from an input or textarea.