Create Timing Variables

We need to specify how long the animation should take, and measure how long it has taken so far.

1. Create two new number variables, animationTime and elapsedTime. Set animationTime to something long for now, like 3, and let elapsedTime start at 0.
2. We can figure out how much time has passed using a handy property of the game called frameDeltaTime. It measures, in seconds, how long each tick takes.
3. Just after the line where you increment the chest’s Y position, increment this.elapsedTime by this.game.frameDeltaTime.

this.elapsedTime += this.game.frameDeltaTime

4. Add another line to log the value of elapsedTime to the console, so that we can see how long the animation currently takes. 

console.log(this.elapsedTime)