JScript ユーザーズ ガイド、for...in ループ

ary = [10, 20, 30];

for (x in ary) {
  WScript.Echo(x + " : " + ary[x]);
}

まんま

var myObject = new Object();

myObject.name  = "James";
myObject.age   = "22";
myObject.phone = "555 1234";

for (prop in myObject) {
  WScript.Echo("プロパティ '" + prop + "' は " + myObject[prop] + "です。");
}