js之for_in

看下面两段代码，体会forin的循环机制：
/*--------------------------------------*/
var x
var mycars = new Array()
mycars[0] = "Saab"
mycars[1] = "Volvo"
mycars[2] = "BMW"

for (x in mycars)
{
document.write(mycars + "<br />")
}
/*---------------result-----------------------*/
Saab,Volvo,BMW
Saab,Volvo,BMW
Saab,Volvo,BMW
/*----------------example2----------------------*/

var x
var mycars = new Array()
mycars[0] = "Saab"
mycars[1] = "Volvo"
mycars[2] = "BMW"

for (x in mycars)
{
document.write(mycars[x] + "<br />")
}
/*---------------result----------------------*/
Saab
Volvo
BMW