判断两个数组

var selectArray = document.getElementsByName("objectprojectinfo");
var selectArray2 = document.getElementsByName("objectprojectinfo");
for(var i=0; i<selectArray.length; i+=3){
    //当前比较的对象
     var curselect =selectArray[i].value;
    for(var j=i+3;j<selectArray2.length;j+=3){
//如果该值已选择
if(curselect==selectArray2[j].value){    parentIndex.showMessageBox('已有'+selectArray2[j].options[selectArray2[j].selectedIndex].text+'变更事项！请另选择！', 3);
   selectArray2[j].focus();
   return false;
}
    }
}