Insert text in a textarea/text input at the cursor, when code is being executed in a Chrome Extension content script

I am making a Chrome extension that places some stored, regularly used bits of text, into text inputs and text areas when a context menu item is chosen.

The way it's set up to work at the moment, there's a line in the content script which takes care of the insertion:

document.activeElement.value = "TEXT TO INSERT" + document.activeElement.value ;

This puts the text at the start of whichever textbox/editable area is selected. It would be desirable to insert the text wherever the user i开发者_如何学Gos currently clicked in the textbox, rather than just at the start.

I have seen lots of examples for inputting text at the cursor/caret, but haven't been able to get them to work from a content script. As this doesn't need to be cross-browser compatible, what's the easiest way to make this text insert at the cursor?

Thanks for your help

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The solution is using the code found at http://www.sitepoint.com/forums/showthread.php?t=709013

Changing the first couple of lines of that script so that they read

function insertAtCaret(text) {
    var txtarea = document.activeElement;

The javascript then doesn't need the id of the selected element declared.

This goes in the content script, along with

chrome.extension.onRequest.addListener(
    function(request, sender, sendResponse) {
insertAtCaret(request.text);
if (request.greeting == "hello")
   sendResponse({farewell: "laters"});
else
  sendResponse({farewell: "byebye"}); // snub them.    
});