<html>
<body>
<p>y = 5, 计算 x = --y, y 和 x 为</p>
<button onclick="myFunction()">点我</button>
<p><strong>注意:</strong> x 和 y的值将会改变。</p>
<p id="demo1"></p>
<p id="demo2"></p>
<script>
function myFunction() {
var y = 5;
var x = --y;
document.getElementById("demo1").innerHTML = y;
document.getElementById("demo2").innerHTML = x;
}
</script>
</body>
</html>