textarea控件表情按光标插入

var start = 0;
var end = 0;
//表情定位光标1
function MoveCursortoPos(id, pos) {//定位光标到某个位置   
    var obj = document.getElementById(id);
    pos = pos ? pos : obj.value.length;
    if (obj.createTextRange) {//IE浏览器
        var range = obj.createTextRange();
        range.moveStart("character", pos);
        range.collapse(true);
        range.select();
    } else {//非IE浏览器
        obj.setSelectionRange(obj.value.length, pos);
    }
    obj.focus();
}
//添加表情
function add(title) {
    var facetitle = "[" + title + "]";
    var textBox = document.getElementById("layim_write");
    var pre = textBox.value.substr(0, start);
    var post = textBox.value.substr(end);
    textBox.value = pre + facetitle + post;
    MoveCursortoPos("layim_write", start + facetitle.length);
   // $("#layim_write").blur();
    $(".layim_facelist").hide();
}
//表情定位光标2
function savePos(textBox) {
    //如果是Firefox(1.5)的话，方法很简单
    if (typeof (textBox.selectionStart) == "number") {
        start = textBox.selectionStart;
        end = textBox.selectionEnd;
    }
        //下面是IE(6.0)的方法，麻烦得很，还要计算上'
'
    else if (document.selection) {
        var range = document.selection.createRange();
        if (range.parentElement().id == textBox.id) {
            // create a selection of the whole textarea
            var range_all = document.body.createTextRange();
            range_all.moveToElementText(textBox);
            //两个range，一个是已经选择的text(range)，一个是整个textarea(range_all)
            //range_all.compareEndPoints()比较两个端点，如果range_all比range更往左(further to the left)，则                //返回小于0的值，则range_all往右移一点，直到两个range的start相同。
            // calculate selection start point by moving beginning of range_all to beginning of range
            for (start = 0; range_all.compareEndPoints("StartToStart", range) < 0; start++)
                range_all.moveStart('character', 1);
            // get number of line breaks from textarea start to selection start and add them to start
            // 计算一下

            for (var i = 0; i <= start; i++) {
                if (textBox.value.charAt(i) == '
')
                    start++;
            }
            // create a selection of the whole textarea
            var range_all = document.body.createTextRange();
            range_all.moveToElementText(textBox);
            // calculate selection end point by moving beginning of range_all to end of range
            for (end = 0; range_all.compareEndPoints('StartToEnd', range) < 0; end++)
                range_all.moveStart('character', 1);
            // get number of line breaks from textarea start to selection end and add them to end
            for (var i = 0; i <= end; i++) {
                if (textBox.value.charAt(i) == '
')
                    end++;
            }
        }
    }
    //document.getElementById("start").value = start;
    //document.getElementById("end").value = end;
}

  <textarea class="layim_write" id="layim_write" onKeydown="savePos(this)"  onKeyup="savePos(this)" onmousedown="savePos(this)" onmouseup="savePos(this)"  onfocus="savePos(this)" ></textarea>