[英]Uncaught TypeError: Cannot read property 'getContext' of null
[英]Uncaught TypeError: Cannot read property 'getContext' of null Node.js
我正在尝试为一个项目创建流式视频,正在包括HTML的node.js中创建,但无法通过此错误完成Uncaught TypeError: Can not read property 'getContext' of null
然后我需要解决该问题,但是我不能,因为我寻求解决方案和这种类型的错误,但是没有一个对我有效,只是我必须在以下几行中进行评论的问题:
var context = canvas.getContext("2d");
canvas.width = 800;
canvas.height = 600;
context.width = canvas.width;
context.height = canvas.height
这是我的proyect的代码:Emitir Video
<canvas style = "display:none;" id "preview" width='1280' height='720'></canvas>
<div id = "logger"></div>
<script type="text/javascript">
var canvas = document.getElementById("preview");
var context = canvas.getContext("2d"); // This is the line that generates the error
canvas.width = 800;
canvas.height = 600;
context.width = canvas.width;
context.height = canvas.height;
var video = document.getElementById("video");
var socket = io();
function logger(msg)
{
$("#logger").text(msg);
}
function loadCam(stream)
{
video.src = window.URL.createObjectURL(stream);
logger('Camara cargada correctamente [OK]');
}
function loadFail()
{
logger('Camara no conectada, Favor Conectela');
}
function viewVideo(video,context)
{
context.drawImage(video,0,0,context.width,context.height);
socket.emit('stream',canvas.toDataURL('image/webp'));
}
$(function(){
navigator.getUserMedia = (navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msgGetUserMedia);
if (navigator.getUserMedia)
{
navigator.getUserMedia({video: true}, loadCam, loadFail);
}
//1000 = 1 Seg.
setInterval(function(){
viewVideo(video,context);
},70);
});
</script>
</body>
</html>
谢谢,我将帮助您。
您需要将id "preview"
更改为id="preview"
,然后可以继续进行下一个错误:)
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