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JavaScript Object-Oriented JavaScript: Challenge Making the Game Interactive handleKeydown() Solution

Posted by Andrew Phythian
Andrew Phythian
19,747 Points

How does this code work?

Given that my app.js code for the 'keydown' event is identical to that shown in the video, how does the second part of my code for the Game.js 'handleKeyDown' method actually work...

handleKeyDown(keydown) {
    if(this.ready == true) {
      if(event.key === 'ArrowRight') {
        // Move right
      } else if (event.key === 'ArrowLeft') {
        // Move left
      } else if (event.key === 'ArrowDown') {
        // Move down
      }
    }
  }

I'm passing 'keydown' as the argument but referencing something different, 'event.key' when checking the arrow direction. I've done a console.log and it works but I'm puzzled why?

1 Answer

Steven Parker
Steven Parker
229,744 Points
Steven Parker
Steven Parker
229,744 Points

Browsers generally create an "event" variable in a handler to reference the event object, as long as that name isn't already being used. But it's not good practice to rely on this. It's much better to use the reference explicitly passed in.

So while it works as-is, it would be cleaner to either rename the argument "keydown" to "event", or to change the references from "event" to "keydown".