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!