textarea光标位置插入文字
各浏览器TextArea获得焦点后的光标位置情况：

textarea.focus()
FireFox: 所有文字结束处
IE: 文字开头
Opera: 文字开头
Chrome: 文字开头
Safari: 文字开头

IE支持document.selection，Firefox，Chrome,Safari以及Opera都有selectionStart和selectionEnd属性。

针对浏览器的特性进行判断并实现，代码如下：

function insertText(obj,str) {if (document.selection) {var sel = document.selection.createRange();sel.text = str;} else if (typeof obj.selectionStart === 'number' && typeof obj.selectionEnd === 'number') {var startPos = obj.selectionStart,endPos = obj.selectionEnd,cursorPos = startPos,tmpStr = obj.value;obj.value = tmpStr.substring(0, startPos) + str + tmpStr.substring(endPos, tmpStr.length);cursorPos += str.length;obj.selectionStart = obj.selectionEnd = cursorPos;} else {obj.value += str;}}function moveEnd(obj){obj.focus();var len = obj.value.length;if (document.selection) {var sel = obj.createTextRange();sel.moveStart('character',len);sel.collapse();sel.select();} else if (typeof obj.selectionStart == 'number' && typeof obj.selectionEnd == 'number') {obj.selectionStart = obj.selectionEnd = len;}｝

参考：
http://foxling.org/js-ajax-dom/cross-browser-cursor-position-in-textarea/