一共三个问题 ：1、 change()函数是1秒钟执行一次，当中的console 语句也应该是每秒输出一次，但在本地执行发现，每次的console语句被执行情况 为什么会这样2、 怎样在每次画图之前清空之前的绘制结果， 现在的是直接绘制在之前的效果上的。3、当setTimeout 这么写时 ，报错如下找了很久都没发现问题出在哪里，为什么会这样的错误这几个问题我想了很久都到底哪里出了问题 ，希望各位大神能够解答下我的疑惑。谢谢！<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>canvas 倒数计时</title></head><body><canvas id="canvas" style="margin-left:200px; margin-top:120px"></canvas><script type="text/javascript"> var HEIGHT = 500; var WIDTH = 700; var r = 4; var R = 5; var MARGIN_TOP = 30; var MARGIN_LEFT = 20; window.onload = function () { var canvas = document.getElementById("canvas"); var context = canvas.getContext("2d"); canvas.height = HEIGHT; canvas.width = WIDTH; var digit = [ [ [0, 0, 1, 1, 1, 0, 0], [0, 1, 1, 0, 1, 1, 0], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 0, 1, 1, 0], [0, 0, 1, 1, 1, 0, 0] ],//0 [ [0, 0, 0, 1, 1, 0, 0], [0, 1, 1, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [1, 1, 1, 1, 1, 1, 1] ],//1 [ [0, 1, 1, 1, 1, 1, 0], [1, 1, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 1, 1, 0, 0, 0], [0, 1, 1, 0, 0, 0, 0], [1, 1, 0, 0, 0, 0, 0], [1, 1, 0, 0, 0, 1, 1], [1, 1, 1, 1, 1, 1, 1] ],//2 [ [1, 1, 1, 1, 1, 1, 1], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 1, 1, 1, 0, 0], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 1, 1, 1, 0] ],//3 [ [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 1, 1, 1, 0], [0, 0, 1, 1, 1, 1, 0], [0, 1, 1, 0, 1, 1, 0], [1, 1, 0, 0, 1, 1, 0], [1, 1, 1, 1, 1, 1, 1], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 1, 1, 1, 1] ],//4 [ [1, 1, 1, 1, 1, 1, 1], [1, 1, 0, 0, 0, 0, 0], [1, 1, 0, 0, 0, 0, 0], [1, 1, 1, 1, 1, 1, 0], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 1, 1, 1, 0] ],//5 [ [0, 0, 0, 0, 1, 1, 0], [0, 0, 1, 1, 0, 0, 0], [0, 1, 1, 0, 0, 0, 0], [1, 1, 0, 0, 0, 0, 0], [1, 1, 0, 1, 1, 1, 0], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 1, 1, 1, 0] ],//6 [ [1, 1, 1, 1, 1, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0], [0, 0, 1, 1, 0, 0, 0], [0, 0, 1, 1, 0, 0, 0], [0, 0, 1, 1, 0, 0, 0], [0, 0, 1, 1, 0, 0, 0] ],//7 [ [0, 1, 1, 1, 1, 1, 0], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 1, 1, 1, 0], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 1, 1, 1, 0] ],//8 [ [0, 1, 1, 1, 1, 1, 0], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [1, 1, 0, 0, 0, 1, 1], [0, 1, 1, 1, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 1, 1, 0], [0, 0, 0, 1, 1, 0, 0], [0, 1, 1, 0, 0, 0, 0] ],//9 [ [0, 0, 0, 0], [0, 0, 0, 0], [0, 1, 1, 0], [0, 1, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 1, 1, 0], [0, 1, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0] ]//: ];
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