Question

Let’s say that I have a block of code like this:

keysPressed = new Object();
document.onkeydown = function(e) {
    keysPressed[e.charCode] = true;
}
document.onkeyup = function(e) {
    keysPressed[e.charCode] = false;
}

This should theoretically leave me with an object where I can go keysPressed.w to check if ‘w’ is currently pressed.

I can see in my JavaScript console that all of the attributes are defined like normal, but whenever I try to access them, it says that they’re undefined. I suspect that the attributes have a local scope inside the functions where they’re defined, and can’t be accessed elsewhere. Is there any way to solve this problem without creating a whole bunch of global variables?

Thanks in advance!

Answer 1

The problem here is that charCode returns a numeric value. So instead of adding a property for w it’s adding an property for the number 87. You want to use String.fromCharCode to get the string representation here

keysPressed = new Object();
document.onkeydown = function(e) {
    keysPressed[String.fromCharCode(e.charCode)] = true;
}
document.onkeyup = function(e) {
    keysPressed[String.fromCharCode(e.charCode)] = false;
}

Now code like the following will work (note the use of upper case W instead of lower)

if (keysPressed.W) {
  ...
}