代码示例:(标识:js_oper_incr_1)
<!DOCTYPE html>
<html>
<body>

<h1>JavaScript 运算符</h1>

<p>在这个例子中,y 在被赋值给 x 之前就被递增了(即预先递增)。</p>

<p id="demo1"></p>
<p id="demo2"></p>

<script>
var y = 5;
var x = ++y;
document.getElementById("demo1").innerHTML = y;
document.getElementById("demo2").innerHTML = x;
</script>

</body>
</html>
运行结果: