Changing the keypress

In an input box or contenteditable=true div, how can I modify a keypress for the letter "a" to return a keybress for the letter "b"? I.e., every time you type the letter "a" in the div, the output is actually the letter "b".

I'm not that concerned with a solution that works in IE--just one that works in Safari, Chrome, & FF.

In Chrome, I can see that a keypress event has the properties "charCode", "keyCode", and "which", all of which get assigned the keypress event number. If I fire an event on a keypress, I can modify these values, but I can't figure out what to return so that the actual key that gets typed is different. For example:

$(window).keypress(function(e){  //$(window) is a jQuery object
    e.charCode = 102;
    e.which = 102;
    e.keyCode = 102;
    console.log(e);
    return e;
});

I can also see that along with charCode, which, and keyCode, there is also an "originalEvent" property which in turn also has these properties. However, I haven't been able to modify those (I tried with things like e.originalEvent.charCode = 102).

You can't change the character or key associated with a key event, or fully simulate a key event. However, you can handle the keypress yourself and manually insert the character you want at the current insertion point/caret. I've provided code to do this in a number of places on Stack Overflow. For a contenteditable element:

• Need to set cursor position to the end of a contentEditable div, issue with selection and range objects

Here's a jsFiddle example: http://www.jsfiddle.net/Ukkmu/4/

For an input:

• Can I conditionally change the character entered into an input on keypress?

• show different keyboard character from the typed one in google chrome

Cross-browser jsFiddle example: http://www.jsfiddle.net/EXH2k/6/

IE >= 9 and non-IE jsFiddle example: http://www.jsfiddle.net/EXH2k/7/

My solution example (change in input[type=text] the character ',' to '.'):

element.addEventListener('keydown', function (event) {
if(event.key === ','){
  setTimeout(function() {
    event.target.value += '.';
  }, 4);
  event.preventDefault();
};