Javascript没有显示在浏览器中 [英] Javascript not showing up in browser
问题描述
我在本地主机上制作我的网络应用程序，但浏览器页面一直显示为空白，我做错了什么？谢谢
< html>
< head>
< script>
window.onload = function（）{
var canvas = document.getElementById（canvas），
ctx = canvas.getContext（2d），
W = window.innerWidth，
H = window.innerHeight;
setInterval（draw，33）;
函数draw（）{
ctx.globalcompositeOperation =source-over;
ctx.fillStyle =black;
ctx.fillRect（0,0，W，H）;
}
}
< / script>
< / head>
< body>
< canvas id =canvas>< / canvas>
你在分配给 onload 的匿名函数中声明了一堆变量。它们不是全局变量。
然后尝试（在一个时间间隔内）将它们作为全局变量来访问。
您在开发人员工具中查看控制台，您应该会看到一堆 ReferenceErrors 。
$ b 移动 setInterval 和绘制函数声明放入您分配给 onload 。
window.onload = function（）{var canvas = document.getElementById（canvas），ctx = canvas.getContext（2d ），W = window.innerWidth，H = window.innerHeight; setInterval（draw，33）;函数draw（）{ctx.globalcompositeOperation =source-over; ctx.fillStyle =black; ctx.fillRect（0，0，W，H）; }}
< canvas id =canvas> < / canvas>
I am making my web app on localhost, but the browser page keeps showing up as blank, what am I doing wrong? Thanks
<html>
<head>
<script>
window.onload = function() {
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
W = window.innerWidth,
H = window.innerHeight;
setInterval(draw, 33);
function draw() {
ctx.globalcompositeOperation = "source-over";
ctx.fillStyle = "black";
ctx.fillRect(0,0,W,H);
}
}
</script>
</head>
<body>
<canvas id="canvas"></canvas>
You declare a bunch of variables inside the anonymous function you assign to onload. They are not globals.
You then try to (on an interval) access them as globals.
If you look at the Console in your developer tools you should expect to see a bunch of ReferenceErrors.
Move setInterval and the draw function declaration inside the anonymous function you assign to onload.
window.onload = function () {
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
W = window.innerWidth,
H = window.innerHeight;
setInterval(draw, 33);
function draw() {
ctx.globalcompositeOperation = "source-over";
ctx.fillStyle = "black";
ctx.fillRect(0, 0, W, H);
}
}
<canvas id="canvas"></canvas>
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