Why doesn't this JavaScript display a confirm box?

function lastCheckInv() {

    document.getElementById("ctl00$ContentPlaceHolderMain$INDet$txtInvNumber").style.background = "yellow";
    document.getElementById("ctl00$ContentPlaceHolderMain$INDet$txtInvNumber").focus();
    document.getElementById("ctl00_ContentPlaceHolderMain_INDet_AddCharges").style.background = "yellow";
    document.getElementById("ctl00_ContentPlaceHolderMain_INDet_lblFreight").style.background = "yellow";
    bRetVal = confirm("Are you sure the information associated with this invoice is correct?");

    return bRetVal;

}

document.getElementById(<%= txtInvNumber.ClientID %>).style.background = "yellow"

<script language="javascript">
function lastCheckInv() {

    document.getElementById("test1").style.background = "yellow";
    document.getElementById("test1").focus();
    document.getElementById("test2").style.background = "yellow";
    document.getElementById("test3").style.background = "yellow";
    bRetVal = confirm("Are you sure?");

    return bRetVal;

}
</script>

<form method="get" onsubmit="return lastCheckInv();">
    <input id="test1" name="test1" value="Hello">
    <input id="test2" name="test2" value="Hi">
    <input id="test3" name="test3" value="Bye">
    <input type="submit" name="Save" value="Save">
</form>

document.getElementById("ctl00_ContentPlaceHolderMain_INDet_lblFreight").style.background = "yellow";

var obj = document.getElementById("ctl00_ContentPlaceHolderMain_INDet_lblFreight");

if(obj)
{
    obj.style.background = "yellow";
}

function lastCheckInv() {

    var myObjs,bRetVal;

    myObjs=[
        "ctl00_ContentPlaceHolderMain_INDet_AddCharges",
        "ctl00_ContentPlaceHolderMain_INDet_lblFreight",
        "ctl00$ContentPlaceHolderMain$INDet$txtInvNumber"
    ];


    bRetVal = confirm("Are you sure the information associated with this invoice is correct?");

    for (var i=0, j=myObjs.length, myElement; i<j; i++){

        myElement=document.getElementById(myObjs[i]);

        if (!myElement){
        // this element is missing
        continue;
        }

        else {

        // apply colour
        myElement.style.background = "yellow";

       // focus the last object in the array

            if (i == (j-1) ){
            myObj.focus();
            }


        }

    }


    return bRetVal;

}

function lastCheckInv()

{
   document.getElementById("ctl00_ContentPlaceHolderMain_INDet_txtInvNumber").style.background = "yellow";
   document.getElementById("ctl00_ContentPlaceHolderMain_INDet_txtInvNumber").focus();
   document.getElementById("ctl00_ContentPlaceHolderMain_INDet_AddCharges").style.background = "yellow";
   document.getElementById("ctl00_ContentPlaceHolderMain_INDet_lblFreight").style.background = "yellow";
   return confirm("Are you sure the information associated with this invoice is correct?");
}