JavaScript获取页面元素

        onload = function () {
            alert(document.getElementById('Button0').value);

            var buttonArr = document.getElementsByName('n1');
            for (var i = 0; i < buttonArr.length; i++) {
                alert(buttonArr[i].value);
            }

            var button = document.getElementsByTagName("input");
            for (var i = 0; i < button.length; i++) {
                alert(button[i].value);
            }
        };

获取页面元素三种方式：

getElementById

getElementsByName

getElementsByTagName