for、for / in循环

1.for循环

循环代码块一定的次数

<!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title></title>
  </head>
  <body>
  <script>
  var cars=new Array()
  cars[0]="Saab"
  cars[1]="BMW"
  cars[2]="Volvo"
  for (var i = 0; i < cars.length; i++) {
    document.write(cars[i]+"<br />")
  }
  </script>
  </body>
</html>

输出：

、

2.for/in循环

循环遍历对象的属性

<!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title></title>
  </head>
  <body>
  <script>
  var cars=new Array()
  cars[0]="Saab"
  cars[1]="BMW"
  cars[2]="Volvo"
  for (x in cars) 
  {
    document.write(cars[x]+"<br />")
  }
  </script>
  </body>
</html>

输出：

在此处两个循环输出效果一样