IE下javascript获取textarea光标的开始结束位置

项目开发中需要计算textarea光标的开始位置与结束位置，以便于在指定位置插入文本。下面这段代码测试通过，能够得到光标的开始位置与结束位置。var er = document.selection.createRange(),start = 0,end = 0;

if(er.parentElement().id === this.id){// create a selection of the whole textareavar er1 = document.body.createTextRange();er1.moveToElementText(this);//两个range，一个是已经选择的text(er)，一个是整个textarea(er1)//er1.compareEndPoints()比较两个端点，如果er1比er更往左(further to the left)，则 //返回小于0的值，则er1往右移一点，直到两个er的start相同。// calculate selection start point by moving beginning of er1 to beginning of erfor (start = 0;er1.compareEndPoints('StartToStart',er) < 0;start++){er1.moveStart('character', 1);}// get number of line breaks from textarea start to selection start and add them to start// 计算一下\nfor (var i = 0; i <= start;i++){if (this.value.charAt(i) == '\n'){start++;}}// create a selection of the whole textareavar er1 = document.body.createTextRange();er1.moveToElementText(this);// calculate selection end point by moving beginning of er1 to end of erfor (end = 0;er1.compareEndPoints('StartToEnd',er) < 0;end++){er1.moveStart('character',1);}// get number of line breaks from textarea start to selection end and add them to endfor (var i = 0;i <= end;i++){if (this.value.charAt(i) == '\n'){end ++;}}}