更新未定义？
我试图在画布上创建一个移动对象，但每次设置的间隔结束时，它都会给出错误：“更新未定义”，即使更新的定义就在初始化之前。如何设置正确调用更新的间隔？
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Test</title>
<meta name="description" content="An HTML5 Test">
<meta name="author" content="William Starkovich">
<link rel="stylesheet" href="css/styles.css?v=1.0">
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var angle = 0.0;
var increment = 0.1;
function incrementAngle(angle, increment){
angle += increment;
if(angle > Math.PI * 2)
angle -= (Math.PI * 2);
}
function update(angle, increment){
incrementAngle(angle, increment);
//get a reference to the canvas
var ctx = $('#canvas')[0].getContext("2d");
//draw a circle
ctx.strokeStyle = "#000000";
ctx.beginPath();
ctx.arc(20, 20, 15, angle, angle + Math.PI, true);
ctx.lineWidth = 5;
ctx.stroke();
ctx.closePath();
}
function init(angle, increment){
update(angle, increment)
setInterval("update(angle, increment)",1000);
}
init(angle, increment);
});
</script>
</head>
<body>
<canvas id="canvas" width="800px" height="100px">
<p>Your browser doesn't support canvas.</p>
</canvas>
</body>
</html>
I'm trying to make a moving object on canvas, but each time the set interval goes off it gives me the error: "update is not defined" even though update's definition is right there before init. How do I get set interval to call update correctly?
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Test</title>
<meta name="description" content="An HTML5 Test">
<meta name="author" content="William Starkovich">
<link rel="stylesheet" href="css/styles.css?v=1.0">
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var angle = 0.0;
var increment = 0.1;
function incrementAngle(angle, increment){
angle += increment;
if(angle > Math.PI * 2)
angle -= (Math.PI * 2);
}
function update(angle, increment){
incrementAngle(angle, increment);
//get a reference to the canvas
var ctx = $('#canvas')[0].getContext("2d");
//draw a circle
ctx.strokeStyle = "#000000";
ctx.beginPath();
ctx.arc(20, 20, 15, angle, angle + Math.PI, true);
ctx.lineWidth = 5;
ctx.stroke();
ctx.closePath();
}
function init(angle, increment){
update(angle, increment)
setInterval("update(angle, increment)",1000);
}
init(angle, increment);
});
</script>
</head>
<body>
<canvas id="canvas" width="800px" height="100px">
<p>Your browser doesn't support canvas.</p>
</canvas>
</body>
</html>
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评论（2）
您似乎正在寻求使用全局变量，那么为什么不一路走下去呢？
http://jsfiddle.net/mblase75/8L62c/3/
You appear to be looking to use global variables, so why not go all the way?
http://jsfiddle.net/mblase75/8L62c/3/
不要在
eval中使用字符串，因为它们是在全局范围内执行的，并且您的函数是在 document.ready 处理程序中定义的。如果您想提供参数，请使用匿名函数：Don't use strings in
evalbecause they are executed in global scope and your function is defined in the document.ready handler. Use an anonymous function if you want to provide arguments: