<p>设置 y=5, 计算出 x=y-2, 并输出结果</p>

<button onclick="myFunction()">点我</button>

<p id="demo"></p>

<script>

function myFunction()

{

    var y=5;

    var x=y-2;

    var demoP=document.getElementById("demo");

    demoP.innerHTML="x=" + x;

}

</script>

​