document.onkeypress is not working, how to fix?

Question

Is there any reason the following code should not return anything in my console log?!

document.onkeypress =  zx();

function zx(){
    console.log(event.keyCode);
} // zx

window.onkeypress also doesn't work.

Other attempts has been made, like these:

document.onkeypress =  zx(event);

function zx(event){
    console.log(event.keyCode);
} // zx

-

document.onkeypress =  zx;

function zx(){
    console.log(event.keyCode);
} // zx

Thanks!

Answer 1

Omit the parenthesis on the call, you do not need to specify them.

Solution:

document.onkeypress =  zx;
function zx(e){
    var charCode = (typeof e.which == "number") ? e.which : e.keyCode
    console.log(charCode);
}

Demo

Answer 2

When attaching a function to event you don't need the ()

Just do:

document.onkeypress =  zx; //note! don't use the ()

function zx(){
    console.log(event.keyCode);
} // zx

if you are using chrome try to catch the right value by

function zx(e){
    var key = e.which || e.keyCode;
    console.log(key);
} // zx