Using a Chrome extension to insert characters into sites such as Facebook - facebook

Question

I have created a chrome extension to allow users to right-click in a textbox, and insert special characters. This works on many sites such as StackOverflow, but does not work on sites such as Facebook. This is because Facebook is not using a standard text box form control. Instead for each line in a text message, it seems to be using a div > div > span > span construct. Is there a way to create a Chrome extension to target page components such as this?
An portion of my Chrome extension code looks like this:
main.js:
chrome.contextMenus.create({
title: "\u038F",
contexts:["editable"],
onclick: function(info, tab){
chrome.tabs.sendMessage(tab.id, {action: "insertCharacter", character: '\u038F'});
}
});
content.js
chrome.extension.onMessage.addListener(function(request, sender, sendResponse){
var objField = document.activeElement;
if (request.action == "insertCharacter"){
insertAtCursor(objField, request.character);
}
});
function insertAtCursor(sField, sValue){
if (sField.selectionStart || sField.selectionStart == '0'){
var nStart = sField.selectionStart;
var nEnd = sField.selectionEnd;
sField.value = sField.value.substring(0, nStart) + sValue + sField.value.substring(nEnd, sField.value.length);
sField.selectionStart = nStart + sValue.length;
sField.selectionEnd = nStart + sValue.length;
}
else {
sField.value += sValue;
}
}
Is there a more general purpose way I can do this to handle various situations on different sites? If not, is there a way to specifically target Facebook as most of the time myself (and likely others) are going to be using my extension on Facebook. (Of course having it work for email sites such as GMail would be a benefit as well).

Answer 1

In case it helps someone else, this is what I modified my code to based on wOxxOm's suggestion:
chrome.extension.onMessage.addListener(function(request, sender, sendResponse){
if (request.action == "insertCharacter"){
insertAtCursor(request.character);
}
});
function insertAtCursor(sValue){
document.execCommand("insertText", false, sValue);
}
It's much more compact than my original approach and insertText handles the selection aspect automatically.