从这里使用：
function insertAtCaret(areaId, text) { var txtarea = document.getElementById(areaId); if (!txtarea) { return; } var scrollPos = txtarea.scrollTop; var strPos = 0; var br = ((txtarea.selectionStart || txtarea.selectionStart == '0') ? "ff" : (document.selection ? "ie" : false)); if (br == "ie") { txtarea.focus(); var range = document.selection.createRange(); range.moveStart('character', -txtarea.value.length); strPos = range.text.length; } else if (br == "ff") { strPos = txtarea.selectionStart; } var front = (txtarea.value).substring(0, strPos); var back = (txtarea.value).substring(strPos, txtarea.value.length); txtarea.value = front + text + back; strPos = strPos + text.length; if (br == "ie") { txtarea.focus(); var ieRange = document.selection.createRange(); ieRange.moveStart('character', -txtarea.value.length); ieRange.moveStart('character', strPos); ieRange.moveEnd('character', 0); ieRange.select(); } else if (br == "ff") { txtarea.selectionStart = strPos; txtarea.selectionEnd = strPos; txtarea.focus(); } txtarea.scrollTop = scrollPos;}<textarea id="textareaid"></textarea><a href="#" onclick="insertAtCaret('textareaid', 'text to insert');return false;">Click Here to Insert</a>
