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Scott McInnis
8,758 PointsCallback without anonymous function wrapper
How would the callback function differ without the anonymous function wrapper since the handleKeydown method is already set to accept the event object directly?
How does the scope of the callback change?
i.e., would the following still work?
document.addEventListener('keydown', game.handleKeydown);
3 Answers
Steven Parker
229,670 PointsYou might have a problem with the calling context if you don't use the wrapper. The method expects "this" to refer to the Game object, which it will if called in the wrapper. But if you use it directly as the callback, "this" will refer to the document object instead.
Scott McInnis
8,758 PointsThanks Steven, that makes perfect sense! For anyone interested, the lesson on js closures helped explain the method scope in a very clear manner.
Ewerton Luna
Full Stack JavaScript Techdegree Graduate 24,031 PointsWhen I first coded this part, I did this passing the game.handleKeydown directly as shown in your example. I kinda understand Steven Parker explanation, but not completely. It is not clear to me why this would reference the event target instead of the game object. I think this is something very important to pay attention to.
Tim Oltman
7,730 PointsI had this problem. I wrote the following code in my app.js file:
document.addEventListener('keydown', game.handleKeydown)
Then in my game.handleKeydown function 'this' referred to the document, not 'game'!
Steven Parker
229,670 PointsThat's exactly what Scott's question is asking about.