监听事件

btn.onclick = function (ev1) {
            // alert(0);
            window.location.href = 'http://www.itlike.com';
        };
btn.onclick = function (ev1) {
            // alert(1);
            window.location.href = 'http://www.baidu.com';
        };
btn.onclick = function (ev1) {
            // alert(1);
            window.location.href = 'http://www.tmall.com';
        }

后面的会覆盖前面的事件

 window.onload = function (ev) {
        var btn = document.getElementById('btn');
        btn.onclick = function (ev1) {
            // alert(0);
            window.location.href = 'http://www.itlike.com';
        };
        btn.onclick = function (ev1) {
            // alert(1);
            window.location.href = 'http://www.baidu.com';
        };
        btn.onclick = function (ev1) {
            // alert(1);
            window.location.href = 'http://www.tmall.com';
        }


       btn.addEventListener('click', function (ev1) {
           alert(0);
       });

        btn.addEventListener('click', function (ev1) {
            alert(1);
        });

        btn.addEventListener('click', function (ev1) {
            alert(2);
        })
    }

0 1 2 跳转页面