Gmail getElementById（'canvas_frame'）在Google Chrome中始终返回null [英] Gmail getElementById('canvas_frame') keeps returning null in Google Chrome

问题描述

我试图为Gmail扩展程序编写JavaScript代码，并且当我试图获取画布框架时，getElementById会一直返回 null 值。

以下是我使用的代码：

  var doc2 = document.getElementById（'canvas_frame'）。contentDocument; 
  

我收到以下错误：

< pre $ Uncaught TypeError：无法读取属性'contentDocument'为null


如何解决这个问题？

解决方案

因为iframe的ID canvas_frame


要获得对相关文档的引用，您可以先尝试获取对的引用， iframe＃canvas_frame ，如果失败，检查当前上下文是否正确：



  var doc2 = document.getElementById（'canvas_frame'）; 
 if（doc2）{
 doc2 = doc2.contentDocument; 
} else if（document.getElementById（'js_frame'））{
 //如果#canvas_frame不存在，但是#js_frame确实存在，那么Gmail会呈现
 // main = top）frame 
 doc2 = document; 
} // else not Gmail's document and doc2 === null 
  




i'm trying to write JavaScript code for a Gmail extension, and when I'm trying to get the canvas frame I, "getElementById" keeps returning the null value.

Here is the code I'm using:

var doc2 = document.getElementById('canvas_frame').contentDocument;

I'm getting the following error:

"Uncaught TypeError: Cannot read property 'contentDocument' of null"

How can I solve this?

解决方案

Because the iframe with ID canvas_frame does not need to exist in Gmail.

To get a reference to the relevant document, you can first try to get a reference to iframe#canvas_frame, and if that fails, check if the current context is correct:

var doc2 = document.getElementById('canvas_frame');
if (doc2) {
    doc2 = doc2.contentDocument;
} else if (document.getElementById('js_frame')) {
    // If #canvas_frame does not exist, but #js_frame does, then Gmail renders
    // everything in the main (=top) frame
    doc2 = document;
} // else not Gmail's document, and doc2 === null

这篇关于Gmail getElementById（'canvas_frame'）在Google Chrome中始终返回null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！