Altering the keypress event of certain keys in JavaScript

I am working on a project which shows the character code of each key that is pressed down inside a text box.

My problem is that when certain keys, namely: Shift, Backspace, Space are pressed down, their character codes appear like: 16, 8, 32.

I want these keys to retain their normal behavior when pressed. So that space causes a space in the text box, and backspace deletes the character, and so on...but the rest of the keys to continue outputting their character code.

How can I go about accomplishing this?

You can just check for the keys and handle accordingly. Here's a demo:

document.getElementById("test-textbox").addEventListener("keypress", function(event) {
    var code = event.keyCode || event.which;
  
    if(code === 16 || code === 8 || code === 32) //check if space, shift, or backspace
        return; //if yes, allow
    
    console.log(code); //if not, log value  
    event.preventDefault(); //prevent entry
});

<input type="text" id="test-textbox">

This will allow the shift, backspace, and space keys to be pressed, but all others will be logged.