为什么我的setinterval只执行了一次？

script type="text/javascript" window.onload = function() { var go = document.getElementById(go); var box = document.getElementById(box); go.onclick = function() { setInterval("hello()", 1000) } } function hello() { box.innerHTML = "hello" + " "; } /script /head body button id="go"开始/button div id="box" style="width: 200px; height: 200px; background-color: aquamarine;"/div /body