Getting an element of a html file from an external js file
Question
I would like help with this problem, i have a file named, index.html, and a file named javascript.js. When i do document.getElementById("canvas"), and then try to change something like the width of the canvas, it gives me a null exception.
Html file
<html>
<body>
<canvas> </canvas>
<script src="javascript.js"></script>
<script>getCanvas.start();</script>
</body>
</html>
JavaScript file
var canvas;
function getCanvas() {
canvas = document.getElementById("canvas");
canvas.width = 500;
}
At line 4, google chrome throws me the following error on the console. Uncaught TypeError: Cannot set the property 'width' of null.
A huge thanks to anybody who helps.
4 answers
solution1
1 2016-06-15 10:21:07
您必须为画布元素指定id
<canvas id="canvas"> </canvas>
solution2
0 2016-06-15 10:21:17
document.getElementById("canvas"); will get you the element which has the id of 'canvas'. Your canvas element does not have the id 'canvas'.
Solution :
<canvas id="canvas"> </canvas>
solution3
0 2016-06-15 10:23:44
document.getElementById("canvas");
This it self say get Element By ID and you didn't give set id.
Try This in your HTML:-
<canvas id="canvas"> </canvas>
solution4
0 2016-06-15 10:32:33
在不更改HTML的情况下，您可以这样使用它：
document.body.getElementsByTagName('canvas');
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