ASP.NET MVC DropDownList causes postbacks which I don't expect - seems to origin from JavaScript

Question

I have a standard form in my MVC project, where I have a DropDownList. When I change the value of the dropdownlist, the whole pages reloads as it results in a postback.

I do not expect this behavior, and I am trying to stop the dropdownlist for doing a postback.

However, this is where it gets weird. I define my dropdownlist in the following way:

@Html.DropDownList("sortOrder", null, new { onchange = "startUpdate(this)" })

Ignoring Javascipt, there is nothing that would expect me to make a postback. If we include the whole form, we can see that is the case as well here:

 @using (var form = Html.BeginForm("Query", "Search", FormMethod.Get, new { id="queryform", name="queryform", onsubmit = "startUpdate(this); return false;"}))
                    {

                                Sorter efter

                                @Html.DropDownList("sortOrder", null, new { onchange = "startUpdate(this)" })

                            
                            

                        
                        
                        
                    }

However, now a smart person might say:

"try to disable JavaScript, and see what happens"

So I did. And then the postback did NOT happen. So my problem, most likely, originates from some JavaScript.

Only problem? I cannot seem to find it.

I have cleared all JavaScript I could imagine that have ANYTHING to do with it, yet it still gives me a postback.

So, sorry, I have to include all my rendered markup, in the hopes that you guys can help me with this big problem (the select html element is called sortOrder):

(I could not copy whole HTML, so I removed some sections - a production version can be seen at http://www.amino.dk/virksomhedsbors/search/query?transactionType=2&text=§orList=&priceFrom=&priceTo= )

 
     
     
     
     
    Virksomheder til salg 
     
     

     
     
     
     
     

     

     

     

     



     
     
     
     
     
     

     
     
     

     

     
     
     
     

     
     
     
     



     




     
     
    Tilføj som søgeagent 
    Virksomheder til salg 
     
     


     
     
    Viser 1 til 30 af i alt 1383 


     

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    Sorter efter  

     
     
     
    BtB og BtC Udklædning, legetøj og kostumer inkl varelager til salg 

     
     
    Midtjylland 
    Udbudspris: 895.000 DKK 
    Forretningsområde: Agenturhandel 
    Velkendt engros firma der handler med udklædning, kostumer og legetøj. Mange faste kunder spredt over hele landet giver en god stabil omsætning. Salget foregår via hjemmeside og kundebesøg... 
     
    Se flere virksomheder til salg inden for:
 
    Agenturhandel 

     
     
    Senest redigeret 16-09-2014 
     
     
    
 
    
 

     

     
     
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    Indskrænk/ændre søgning 
     

     
    Din rolle er:
    Køber     Sælger
 
    
 
    Søgeord:
 
    
 
    
 
    Forretningsområder:
 
    Avanceret ► Alle er påkrævet (OG-søgning) 
     
     Transportmiddelindustri 
     
     


    
 
    Vis avancerede kriterier ► 
    Skjul avancerede kriterier ◄
 
    
 
     
    Beliggenhed:
 
     

     
     
     Nordjylland 
     
     
     Midtjylland 
     
     
     Syd- og Sønderjylland 
     
     
     Fyn 
     
     
     Sjælland, Øerne og Bornholm 
     
     
     Storkøbenhavn 
     
     
     Ikke oplyst 
     
     
     Hele landet 
     
     
     Udlandet 
     

    
 
    Opererer i:
 
    Avanceret ► Alle er påkrævet (OG-søgning) 
     
     
     
     Nordjylland 
     
     
     Midtjylland 
     
     
     Syd- og Sønderjylland 
     
     
     Fyn 
     
     
     Sjælland, Øerne og Bornholm 
     
     
     Storkøbenhavn 
     
     
     Ikke oplyst 
     
     
     Hele landet 
     
     
     Udlandet 
     


    
 
    Prisinterval:
 
     til  
    
 
    
 
    Etableringsår:
 
     til  
    
 
    
 
    Virksomheden skal kunne flyttes:
 
     Ikke vigtigt
 
     Nej
 
     Ja
 
    
 
    Sælgerfinansiering skal tilbydes:
 
     Ikke vigtigt
 
     Nej
 
     Ja
 
    
 
    Sorter efter

I am lost. I have been searching for hours now, and I cannot find that stupid JS that causes the postback. ANY ideas? It would be a tremendous help.

EDIT:

In the code, the startUpdate is refered. I tried to delete it, and I still got postback. Here is the code though:

 function startUpdate(sender) {
            if (tmr != null) clearTimeout(tmr);
            tmr = setTimeout("updateSearch()", 700);
        }

        function updateSearch() {
            tmr = null;
            searchParams.transactiontype = $("input[name=transactionType]:checked").val();
            searchParams.text = $("input[name=text]").val();
            var sct = "";
            $("input[name=sectors]:checked").each(function() { sct += $(this).val() + ","; });
            searchParams.sector = sct;
            searchParams.allsectorsrequired = $("#allSectorsRequired").attr("checked") == "checked" ? "true" : "";
            var rgn = "";
            $("input[name=regions]:checked").each(function() { rgn += $(this).val() + ","; });
            searchParams.region = rgn;
            var orgn = "";
            $("input[name=operatingRegions]:checked").each(function() { orgn += $(this).val() + ","; });
            searchParams.operatingregion = orgn;
            searchParams.alloperatingregionsrequired = $("#allOperatingRegionsRequired").attr("checked") == "checked" ? "true" : "";
            searchParams.priceFrom = $("input[name=priceFrom]").val();
            searchParams.priceTo = $("input[name=priceTo]").val();
            searchParams.yearFrom = $("input[name=yearFrom]").val();
            searchParams.yearTo = $("input[name=yearTo]").val();
            searchParams.canMove = $("input[name=canMove]:checked").val();
            searchParams.financingavailable = $("input[name=financingAvailable]:checked").val();
            searchParams.orderby = $("select[name=sortOrder]").val();

            for (var key in searchParams) {
                if ((!psp || psp[key] != searchParams[key]) && searchParams[key]) {
                    _gaq.push(['_trackEvent', 'Vbørs Søg autoupdate', key, searchParams[key]]);
                }
            }
            psp = $.extend({}, searchParams);

            $("#searchResults").load("@Url.Action("SearchJSON", "Search")", searchParams, searchCallback);

            var tttxt = " til salg";
            if (searchParams.transactiontype != 2) tttxt = " købes";

            if (searchParams.text.length > 0) {
                $("#searchtitle").text(searchParams.text + tttxt);
                document.title = searchParams.text + tttxt;
            }
        }

emerson.marini · Accepted Answer

Based on what I posted in the comments, somehow (you may know where this is happening in your code) your onchange event handler is being changed, from startUpdate(this) to top.location.href=sortLink.replace("{sortOrder}", this.value);.

So, when the select changes, it's replacing the page URL, which obviously cause a refresh (by GET).

ASP.NET MVC DropDownList causes postbacks which I don't expect - seems to origin from JavaScript

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