Inserting text at cursor

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Problem

How do I insert some text at cursor position, just as if user typed it?

Solution

Let's say you have a focused <textbox> in current document. The following function will insert aText string at the cursor position.

function insertText(aText) {
  try {
    var command = "cmd_insertText";
    var controller = document.commandDispatcher.getControllerForCommand(command);
    if (controller && controller.isCommandEnabled(command)) {
      controller = controller.QueryInterface(Components.interfaces.nsICommandController);
      var params = Components.classes["@mozilla.org/embedcomp/command-params;1"];
      params = params.createInstance(Components.interfaces.nsICommandParams);
      params.setStringValue("state_data", aText);
      controller.doCommandWithParams(command, params);
    }
  }
  catch (e) {
    dump("Can't do cmd_insertText! ");
    dump(e+"\n")
  }
}

Known restriction: <textbox> must be focused. If it isn't, you have to focus it temporarily.