How to prevent default event for all cases of switch instruction

Question

When dealing with a lot of possible keyCode (ex : for hotkeys), we'd like to use a switch statement.

We don't want to prevent all combinations of Ctrl + another key to preserve other constructor hotkeys.

We'd like to prevent the default action only for defined cases. But how to do that once ?

I think I'm missing something really obvious.

document.addEventListener("keydown", function(e) {
  var key = e.keyCode || e.which;
  if (!e.ctrlKey) return false;

    switch(key) {
      case 109: e.preventDefault(); scale(-1); break;
      case 107: e.preventDefault(); scale(1); break;
      case 96: e.preventDefault(); scale(0);break;
      case 78: e.preventDefault(); newFile();break;
      case 79: e.preventDefault(); openFile();break;
      case 80: e.preventDefault(); printFile();break;
      case 83: e.preventDefault(); saveFile();break;
      case 66: e.preventDefault(); command("bold");break;
      case 73: e.preventDefault(); command("italic");break;
      case 85: e.preventDefault(); command("underline");break;
      case 76: e.preventDefault(); command("justifyLeft");break;
      case 69: e.preventDefault(); command("justifyCenter");break;
      case 82: e.preventDefault(); command("justifyRight");break;
      case 74: e.preventDefault(); command("justifyFull");break;
      case 90: e.preventDefault(); clipboard.undo();break;
      case 89: e.preventDefault(); clipboard.redo();break;
      default: console.log("Key pressed n°", key)
    }
}, false);

Answer 1

You can simply use a variable prevent that is only set to true in the default case. Then do e.preventDefault() after the switch statement, as follows:

document.addEventListener("keydown", function(e) {
  var key = e.keyCode || e.which;
  if (!e.ctrlKey) return false;

    var prevent = true;

    switch(key) {
      case 109: scale(-1); break;
      case 107: scale(1); break;
      case 96: scale(0);break;
      case 78: newFile();break;
      case 79: openFile();break;
      case 80: printFile();break;
      case 83: saveFile();break;
      case 66: command("bold");break;
      case 73: command("italic");break;
      case 85: command("underline");break;
      case 76: command("justifyLeft");break;
      case 69: command("justifyCenter");break;
      case 82: command("justifyRight");break;
      case 74: command("justifyFull");break;
      case 90: clipboard.undo();break;
      case 89: clipboard.redo();break;
      default: prevent = false; console.log("Key pressed n°", key); break;
    }

    if (prevent) e.preventDefault();
}, false);