javascript 代码：【复制】 
 /*以下代码实现在textarea中按tab键功能*/
        function editTab() {
            var code, sel, tmp, r
            var tabs = ""
            //event.returnValue = false
            sel = event.srcElement.document.selection.createRange()
            r = event.srcElement.createTextRange()

            switch (event.keyCode) {
                case (8):
                    if (!(sel.getClientRects().length > 1)) {
                        event.returnValue = true
                        return
                    }
                    code = sel.text
                    tmp = sel.duplicate()
                    tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top)
                    sel.setEndPoint("startToStart", tmp)
                    sel.text = sel.text.replace(/^/t/gm, "")
                    code = code.replace(/^/t/gm, "").replace(//r/n/g, "/r")
                    r.findText(code)
                    r.select()
                    break
                case (9):
                    if (sel.getClientRects().length > 1) {
                        code = sel.text
                        tmp = sel.duplicate()
                        tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top)
                        sel.setEndPoint("startToStart", tmp)
                        sel.text = "/t" + sel.text.replace(//r/n/g, "/r/t")
                        code = code.replace(//r/n/g, "/r/t")
                        r.findText(code)
                        r.select()
                    }
                    else {
                        sel.text = "/t"
                        sel.select()
                    }
                    break
                case (13):
                    tmp = sel.duplicate()
                    tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top)
                    tmp.setEndPoint("endToEnd", sel)

                    for (var i = 0; tmp.text.match(/^[/t]+/g) && i < tmp.text.match(/^[/t]+/g)[0].length; i++) tabs += "/t"
                    sel.text = "/r/n" + tabs
                    sel.select()
                    break
                default:
                    event.returnValue = true
                    break
            }
        }


        function testTab() {
            var sel = document.selection.createRange();
            if (event.shiftKey && event.keyCode == 9) {
                sel.move("character", -4);
                sel.select();
                event.returnValue = false;
                return;
            }
            if (event.keyCode == 9) {
                sel.text = "/u0020/u0020/u0020/u0020";
                //sel.move("character",4);   
                sel.select();
                event.returnValue = false;
            }
        }


        function testTab() {
            var sel = document.selection.createRange();
            var mytext = sel.text;
            var i, j, k;
            if (event.shiftKey && event.keyCode == 9) {
                arr = mytext.split(String.fromCharCode(13, 10))
                mytext = ""

                for (k = 0; k < arr.length; k++) {

                    for (j = 1; j <= 4; j++) {
                        if (arr[k].substr(0, 1) == "/u0020") {
                            arr[k] = arr[k].slice(1)
                        }
                    }

                    mytext += arr[k] + ((k == (arr.length - 1)) ? "" : String.fromCharCode(13, 10));
                }
                with (sel) {
                    sel.text = mytext;
                    collapse(true)
                    moveEnd("character", 0)
                    moveStart("character", (mytext.length) * -1)
                    select()
                }

                window.event.cancelBubble = true;
                event.returnValue = false;
                return;
            }
            if (event.keyCode == 9) {
                arr = mytext.split(String.fromCharCode(13, 10))
                mytext = ""
                for (j = 0; j < arr.length; j++) {

                    mytext += "/u0020/u0020/u0020/u0020" + arr[j] + ((j == (arr.length - 1)) ? "" : String.fromCharCode(13, 10));
                }


                with (sel) {
                    sel.text = mytext;
                    collapse(true)
                    moveEnd("character", 0)
                    moveStart("character", (mytext.length - 4) * -1)
                    select()
                }

                window.event.cancelBubble = true;
                event.returnValue = false;
                return;
            }
        }

        function editTab() {

            var code, sel, tmp, r
            var tabs = ""
            event.returnValue = false
            sel = event.srcElement.document.selection.createRange()
            r = event.srcElement.createTextRange()

            switch (event.keyCode) {
                case (8):
                    if (!(sel.getClientRects().length > 1)) {
                        event.returnValue = true
                        return
                    }
                    code = sel.text
                    tmp = sel.duplicate()
                    tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top)
                    sel.setEndPoint("startToStart", tmp)
                    sel.text = sel.text.replace(/^/t/gm, "")
                    code = code.replace(/^/t/gm, "").replace(//r/n/g, "/r")
                    r.findText(code)
                    r.select()
                    break
                case (9):
                    if (sel.getClientRects().length > 1) {
                        code = sel.text
                        tmp = sel.duplicate()
                        tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top)
                        sel.setEndPoint("startToStart", tmp)
                        sel.text = "/t" + sel.text.replace(//r/n/g, "/r/t")
                        code = code.replace(//r/n/g, "/r/t")
                        r.findText(code)
                        r.select()
                    }
                    else {
                        sel.text = "/t"
                        sel.select()
                    }
                    break
                case (13):
                    tmp = sel.duplicate()
                    tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top)
                    tmp.setEndPoint("endToEnd", sel)

                    for (var i = 0; tmp.text.match(/^[/t]+/g) && i < tmp.text.match(/^[/t]+/g)[0].length; i++) tabs += "/t"
                    sel.text = "/r/n" + tabs
                    sel.select()
                    break
                default:
                    event.returnValue = true
                    break
            }
        }


        //截获了Tab按键，其他的textarea框不进行此配置
        //下面的代码就是为了实现这个功能，原理很简单，采用上一行的缩进就行
        //只要在html中插入脚本调用set_tab_indent_for_textareas()函数就可以了
        //注1：需要jQuery支持，如果不喜欢jQuery改成裸javascript也很方便的
        //兼容firefox和IE！

        /*------selection operations-------*/
        function insertAtCursor(obj, txt) {
            obj.focus();
            //IE support
            if (document.selection) {
                sel = document.selection.createRange();
                sel.text = txt;
            }
            //MOZILLA/NETSCAPE support
            else {
                var startPos = obj.selectionStart;
                var scrollTop = obj.scrollTop;
                var endPos = obj.selectionEnd;
                obj.value = obj.value.substring(0, startPos) + txt + obj.value.substring(endPos, obj.value.length);
                startPos += txt.length;
                obj.setSelectionRange(startPos, startPos);
                obj.scrollTop = scrollTop;
            }
        }
        function getCaretPos(ctrl) {
            var caretPos = 0;
            if (document.selection) {
                // IE Support
                var range = document.selection.createRange();
                // We'll use this as a 'dummy'
                var stored_range = range.duplicate();
                // Select all text
                stored_range.moveToElementText(ctrl);
                // Now move 'dummy' end point to end point of original range
                stored_range.setEndPoint('EndToEnd', range);
                // Now we can calculate start and end points
                ctrl.selectionStart = stored_range.text.length - range.text.length;
                ctrl.selectionEnd = ctrl.selectionStart + range.text.length;
                caretPos = ctrl.selectionStart;
            } else if (ctrl.selectionStart || ctrl.selectionStart == '0')
            // Firefox support
                caretPos = ctrl.selectionStart;
            return (caretPos);
        }

        function getCurrentLineBlanks(obj) {
            var pos = getCaretPos(obj);
            var str = obj.value;
            var i = pos - 1;
            while (i >= 0) {
                if (str.charAt(i) == '/n')
                    break;
                i--;
            }
            i++;
            var blanks = "";
            while (i < str.length) {
                var c = str.charAt(i);
                if (c == ' ' || c == '/t')
                    blanks += c;
                else
                    break;
                i++;
            }
            return blanks;
        }

        function set_tab_indent_for_textareas() {
            /* set all the tab indent for all the text areas */
            $("textarea").each(function() {
                $(this).keydown(function(eve) {
                    if (eve.target != this) return;
                    if (eve.keyCode == 13)
                        last_blanks = getCurrentLineBlanks(this);
                    else if (eve.keyCode == 9) {
                        eve.preventDefault();
                        insertAtCursor(this, "  ");
                        this.returnValue = false;
                    }
                }).keyup(function(eve) {
                    if (eve.target == this && eve.keyCode == 13)
                        insertAtCursor(this, last_blanks);
                });
            });
        }

    </script>