<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Planets</title>
<script>
//网页加载完成后再执行代码
function init (){
var planet = document.getElementById("greenplanet");
planet.innerHTML = "Red alert: hit by phase fire!";
}
window.onload = init;
</script>
</head>
<body>
<h1>Green Planet</h1>
<p id="greenplanet">All is well</p>
<h1>Red planet</h1>
<p id="redplanet">Nothing to report</p>
<h1>Blue planet</h1>
<p id="blueplanet">All system A-OK</p>
</body>
</html>