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document.getElementById is null

Posted By:      Posted Date: August 29, 2010    Points: 0   Category :ASP.Net
Background I have a Firefox browser with many tabs opened. One of the tabs is displaying a website having data I want to scrape from. I want to take certain data values, compile statistics, and redisplay the information in a newly created popup. The other tabs are unimportant but it would be nice if I could work in others while I am gathering my data (focus moved away from the data window). When focus is on the tab with data, I execute an extension I am building from the tools menu. This starts my output popup window. At the bottom of the popup I have timer START and STOP buttons. When I push the START button, a timer starts controlling a periodic page scrape every few seconds. This webpage with the data is updated in real time via innerHTML which is why I need a timer to scrape the values every few seconds. CurrentlyAnyway, I can locate the window tab that has my data in javascrip.(not sure if this is pertinent or not.) I am confused though how JS knows what tab I am interested in to scrape my data from. I have tried using variants of document.getElementById() but no matter what I do the return is "null". Does somebody know enough to assist? I have taught myself how to do all this in a month so I am nubie all the way. Thanks !Additional Info I have tried the following and all give null returns. var x=window.opener.document.getElementById('active').innerHTML; var x=

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