以下实例中参数 a 将返回 undefined - 在线编辑器

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <script type="text/javascript">
    function getValue() {
      var a, b, c;
      a = void(b = 5, c = 7);
      document.write('a = ' + a + ' b = ' + b + ' c = ' + c);
    }
  </script>
</head>
<body>

  <p>点击以下按钮查看结果：</p>
  <form>
    <input type="button" value="点我" onclick="getValue();" />
  </form>

</body>
</html>
​x
 
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <script type="text/javascript">
    function getValue() {
      var a, b, c;
      a = void(b = 5, c = 7);
      document.write('a = ' + a + ' b = ' + b + ' c = ' + c);
    }
  </script>
</head>
<body>
​
  <p>点击以下按钮查看结果：</p>
  <form>
    <input type="button" value="点我" onclick="getValue();" />
  </form>
​
</body>
</html>