for(变量 in 集合或对象) {
执行语句块
}
<script language="javascript">
var as= [1,4,5,6],
output="";
for(var x in as){
output += " x= " + as[x];
}
alert(output);
</script>
<script language="javascript">
var as={id:5, name:'test'};
output="";
for(var x in as){
output += x+"="+as[x];
}
alert(output);
</script>