for in 次次多循环一次

<script type="text/javascript">

var x

var mycars = new Array()

mycars[0] = "Saab"

mycars[1] = "Volvo"

mycars[2] = "BMW"

for (x in mycars)

{

document.write(mycars[x] + "<br />");

}

</script>

?

调试发现会多进入一次循环.