jq 点击在输入框光标位置插入内容

<button type="button" onclick="setLabel(this);" data-val="插入内容">按钮</button>
<input type="text"  id="share_title">

function setLabel(obj) {
    var val = $(obj).attr('data-val');
    $('#share_title').insertAtFocus(val);
}
(function($){
    $.fn.extend({
        insertAtFocus: function(myValue){
            var $t=$(this)[0];
            if (document.selection) {
                this.focus();
                sel = document.selection.createRange();
                sel.text = myValue;
                this.focus();
            }
            else
            if ($t.selectionStart || $t.selectionStart == '0') {
                var startPos = $t.selectionStart;
                var endPos = $t.selectionEnd;
                var scrollTop = $t.scrollTop;
                $t.value = $t.value.substring(0, startPos) + myValue + $t.value.substring(endPos, $t.value.length);
                this.focus();
                $t.selectionStart = startPos + myValue.length;
                $t.selectionEnd = startPos + myValue.length;
                $t.scrollTop = scrollTop;
            }
            else {
                this.value += myValue;
                this.focus();
            }
        }
    })
})(jQuery);