Gmail Getelementbyid('canvas_frame') Keeps Returning Null In Google Chrome

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 usin

Solution 1:

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;
} elseif (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