往textarea中光标所在位置插入文本

来自于http://www.oschina.net/code/snippet_1780998_36843

$(".addFullIn").click( function () { 
        $(".questionName").insertContent("( )");
    });
//$(".addFullIn")为点击按钮
//$(".questionName")为要插入的文本框
//insertContent("( )")括号内为要插入的内容
    (function ($) {
        $.fn.extend({
            insertContent: function (myValue, t) {
                var $t = $(this)[0];
                if (document.selection) { // ie
                    this.focus();
                    var sel = document.selection.createRange();
                    sel.text = myValue;
                    this.focus();
                    sel.moveStart('character', -l);
                    var wee = sel.text.length;
                    if (arguments.length == 2) {
                        var l = $t.value.length;
                        sel.moveEnd("character", wee + t);
                        t <= 0 ? sel.moveStart("character", wee - 2 * t
                                - myValue.length) : sel.moveStart(
                                "character", wee - t - myValue.length);
                        sel.select();
                    }
                } else if ($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;
                    if (arguments.length == 2) {
                        $t.setSelectionRange(startPos - t,
                                $t.selectionEnd + t);
                        this.focus();
                    }
                } else {
                    this.value += myValue;
                    this.focus();
                }
            }
        })
})(jQuery);