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代码说明：

说明：  HTML5 canvas小人推箱子小游戏，原生JS编写，用键盘上的上、下、左、右键移动小人，把箱子全部推到小球的位置即可过关。箱子只可向前推，不能往后拉，并且小人一次只能推动一个箱子。(HTML5 canvas small person push box games, native JS programming, using the keyboard up, down, left, right keys to move the small person, the box all pushed to the position of the ball can pass. The box can only be pushed forward, not backward, and the person can only push one box at a time.)