<input type="text" name="name" value="0" id="txt" />
<script type="text/javascript">

        window.onload = function () {

            setInterval(function () {

                //获取文本框对象

                var obj = document.getElementById('txt');

                //获取value值

                var txtvalue = parseInt(obj.value);

                obj.value = txtvalue = txtvalue + 1;

            },1000);

        }

    </script>

function f1() {

    alert('嘎嘎');

}

 //计时器,返回值是该计时器的id

 var setId = window.setInterval(f1, 2000);

//清除计时器方法,参数是一个计时器的id,清除计时器

 window.clearInterval(setId);

//这个计时器就执行一次

var setId= setTimeout(function () {

    alert('加载了');

}, 1000);

clearTimeout(setId);//清除计时器

<input type="button" name="name" value="向左走" id="btnLeft" />

    <input type="button" name="name" value="向右走" id="btnRight" />

<script type="text/javascript">

        var def = 'left';

        function f1() {

            def = 'left';

        }

        function f2() {

            def = 'right';

        }

        window.onload = function () {

            setInterval(function () {

                //获取标题内容

                var tit = document.title;

                if (def == 'left') {

                    document.title = tit.substr(1) + tit.charAt(0);

                } else if (def == 'right') {

                    document.title = tit.charAt(tit.length - 1) + tit.substr(0, tit.length - 1);

                }

            }, 1000);

            document.getElementById('btnLeft').onclick = f1;

            document.getElementById('btnRight').onclick = f2;

        };

    </script>