Call ASP NET function from JavaScript

Question

I m writing a web page in ASP NET  I have some JavaScript code  and I have a submit button with a click event   Is it possible to call a method I created in ASP with JavaScript s click event

User · Answer

This reply works like a breeze for me thanks cross browser:

The __doPostBack() method works well.

Another solution (very hackish) is to simply add an invisible ASP button in your markup and click it with a JavaScript method.

<div style="display: none;"> 
    <asp:Button runat="server" ... OnClick="ButtonClickHandlerMethod" /> 
</div>

From your JavaScript, retrieve the reference to the button using its ClientID and then call the .Click() method on it:

var button = document.getElementByID(/* button client id */); 

button.Click();

Blockquote

User · Answer

Add this line to page load if you are getting object expected error   ClientScript GetPostBackEventReference this

User · Answer

If the   doPostBack function is not generated on the page you need to insert a control to force it like this    lt asp Button ID  btnJavascript  runat  server  UseSubmitBehavior  false    gt

User · Answer

Try this   if  ClientScript IsStartupScriptRegistered  window          Page ClientScript RegisterStartupScript this GetType     window    pop      true       Or this  Response Write   lt script gt alert  Hello World    lt  script gt       Use the OnClientClick property of the button to call JavaScript functions

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I try this and so I could run an Asp Net method while using jQuery    Do a page redirect in your jQuery code  window location    Page aspx key 1    Then use a Query String in Page Load  protected void Page Load object sender  EventArgs e        if  Request QueryString  key      null                string key  Request QueryString  key            if  key   1                            Some code                      So no need to run an extra code

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You can do it asynchronously using  NET Ajax PageMethods  See here or here

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The Microsoft AJAX library will accomplish this  You could also create your own solution that involves using AJAX to call your own aspx  as basically  script files to run  NET functions    This is the library called AjaxPro which was written an MVP named Michael Schwarz  This was library was not written by Microsoft   I have used AjaxPro extensively  and it is a very nice library  that I would recommend for simple callbacks to the server  It does function well with the Microsoft version of Ajax with no issues  However  I would note  with how easy Microsoft has made Ajax  I would only use it if really necessary  It takes a lot of JavaScript to do some really complicated functionality that you get from Microsoft by just dropping it into an update panel

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I think blog post How to fetch  amp  show SQL Server database data in ASP NET page using Ajax  jQuery  will help you   JavaScript Code   lt script src  http   code jquery com jquery-3 3 1 js    gt   lt script language  javascript  type  text javascript  gt       function GetCompanies                 UpdatePanel   html   lt div style  text-align center  background-color yellow  border 1px solid red  padding 3px  width 200px  gt Please Wait    lt  div gt               ajax               type   POST               url   Default aspx GetCompanies               data                    dataType   json               contentType   application json  charset utf-8               success  OnSuccess              error  OnError                        function OnSuccess data            var TableContent     lt table border  0  gt                                       lt tr gt                                           lt td gt Rank lt  td gt                                           lt td gt Company Name lt  td gt                                           lt td gt Revenue lt  td gt                                           lt td gt Industry lt  td gt                                       lt  tr gt            for  var i   0  i  lt  data d length  i                  TableContent      lt tr gt                                           lt td gt    data d i  Rank    lt  td gt                                           lt td gt   data d i  CompanyName   lt  td gt                                           lt td gt   data d i  Revenue   lt  td gt                                           lt td gt   data d i  Industry   lt  td gt                                       lt  tr gt                      TableContent      lt  table gt                 UpdatePanel   html TableContent              function OnError data            lt  script gt    ASP NET Server Side Function   WebMethod   ScriptMethod ResponseFormat  ResponseFormat Json   public static List lt TopCompany gt  GetCompanies         System Threading Thread Sleep 5000       List lt TopCompany gt  allCompany   new List lt TopCompany gt         using  MyDatabaseEntities dc   new MyDatabaseEntities                  allCompany   dc TopCompanies ToList              return allCompany

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Static  strongly-typed programming has always felt very natural to me  so at first I resisted learning JavaScript  not to mention HTML and CSS  when I had to build web-based front-ends for my applications  I would do anything to work around this like redirecting to a page just to perform and action on the OnLoad event  as long as I could code pure C    You will find however that if you are going to be working with websites  you must have an open mind and start thinking more web-oriented  that is  don t try to do client-side things on the server and vice-versa   I love ASP NET webforms and still use it  as well as MVC   but I will say that by trying to make things simpler and hiding the separation of client and server it can confuse newcomers and actually end up making things more difficult at times   My advice is to learn some basic JavaScript  how to register events  retrieve DOM objects  manipulate CSS  etc   and you will find web programming much more enjoyable  not to mention easier   A lot of people mentioned different Ajax libraries  but I didn t see any actual Ajax examples  so here it goes   If you are not familiar with Ajax  all it is  is making an asynchronous HTTP request to refresh content  or perhaps perform a server-side action in your scenario  without reloading the entire page or doing a full postback   Client-Side    lt script type  text javascript  gt  var xmlhttp   new XMLHttpRequest       Create object that will make the request xmlhttp open  GET    http   example org api service    true       configure object  method  URL  async  xmlhttp send       Send request  xmlhttp onstatereadychange   function        Register a function to run when the state changes  if the request has finished and the stats code is 200  OK   Write result to  lt p gt      if  xmlhttp readyState    4  amp  amp  xmlhttp statsCode    200              document getElementById  resultText   innerHTML   xmlhttp responseText            lt  script gt    That s it  Although the name can be misleading the result can be in plain text or JSON as well  you are not limited to XML  jQuery provides an even simpler interface for making Ajax calls  among simplifying other JavaScript tasks    The request can be an HTTP-POST or HTTP-GET and does not have to be to a webpage  but you can post to any service that listens for HTTP requests such as a RESTful API  The ASP NET MVC 4 Web API makes setting up the server-side web service to handle the request a breeze as well  But many people do not know that you can also add API controllers to web forms project and use them to handle Ajax calls like this   Server-Side   public class DataController   ApiController       public HttpResponseMessage lt string   gt  Get                 HttpResponseMessage lt string   gt  response   new HttpResponseMessage lt string   gt               Repository Get true               new MediaTypeHeaderValue  application json                       return response            Global asax  Then just register the HTTP route in your Global asax file  so ASP NET will know how to direct the request   void Application Start object sender  EventArgs e        RouteTable Routes MapHttpRoute  Service    api  controller   id         With AJAX and Controllers  you can post back to the server at any time asynchronously to perform any server side operation  This one-two punch provides both the flexibility of JavaScript and the power the C    ASP NET  giving the people visiting your site a better overall experience  Without sacrificing anything  you get the best of both worlds   References   Ajax  jQuery Ajax  Controller in Webforms

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You can use PageMethods Your C  method Name in order to access C  methods or VB NET methods into JavaScript

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You can also get it by just adding this line in your JavaScript code   document getElementById   lt   btnName ClientID  gt    click     I think this one is very much easy

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Regarding   var button   document getElementById    Button client id       button click      It should be like   var button   document getElementById   lt   formID ClientID  gt       Where formID is the ASP NET control ID in the  aspx file

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The simplest and best way to achieve this is to use the onmouseup   JavaScript event rather than onclick    That way you will fire JavaScript after you click and it won t interfere with the ASP OnClick   event

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I m trying to implement this but it s not working right  The page is   posting back  but my code isn t getting executed  When i debug the   page  the RaisePostBackEvent never gets fired  One thing i did   differently is I m doing this in a user control instead of an aspx   page    If anyone else is like Merk  and having trouble over coming this  I have a solution   When you have a user control  it seems you must also create the PostBackEventHandler in the parent page  And then you can invoke the user control s PostBackEventHandler by calling it directly  See below   public void RaisePostBackEvent string  arg        UserControlID RaisePostBackEvent  arg       Where UserControlID is the ID you gave the user control on the parent page when you nested it in the mark up   Note  You can also simply just call methods belonging to that user control directly  in which case  you would only need the RaisePostBackEvent handler in the parent page    public void RaisePostBackEvent string  arg        UserControlID method1        UserControlID method2

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The Microsoft AJAX library will accomplish this  You could also create your own solution that involves using AJAX to call your own aspx  as basically  script files to run  NET functions   I suggest the Microsoft AJAX library  Once installed and referenced  you just add a line in your page load or init   Ajax Utility RegisterTypeForAjax GetType YOURPAGECLASSNAME     Then you can do things like    lt Ajax AjaxMethod   gt    Public Function Get5   AS Integer     Return 5 End Function   Then  you can call it on your page as   PageClassName Get5 javascriptCallbackFunction     The last parameter of your function call must be the javascript callback function that will be executed when the AJAX request is returned

User · Answer

The   doPostBack   method works well   Another solution  very hackish  is to simply add an invisible ASP button in your markup and click it with a JavaScript method    lt div style  display  none   gt      lt asp Button runat  server      OnClick  ButtonClickHandlerMethod    gt   lt  div gt    From your JavaScript  retrieve the reference to the button using its ClientID and then call the  click   method on it   var button   document getElementById    button client id       button click

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Please try this    lt    Page ClientScript GetPostBackEventReference ddlVoucherType  String Empty    gt     ddlVoucherType is a control which the selected index change will call    And you can put any function on the selected index change of this control

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You might want to create a web service for your common methods  Just add a WebMethodAttribute over the functions you want to call  and that s about it  Having a web service with all your common stuff also makes the system easier to maintain

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Well  if you don t want to do it using Ajax or any other way and just want a normal ASP NET postback to happen  here is how you do it  without using any other libraries    It is a little tricky though        i  In your code file  assuming you are using C  and  NET 2 0 or later  add the following Interface to your Page class to make it look like  public partial class Default   System Web UI Page  IPostBackEventHandler     ii  This should add  using Tab-Tab  this function to your code file   public void RaisePostBackEvent string eventArgument        iii  In your onclick event in JavaScript  write the following code   var pageId     lt     Page ClientID   gt      doPostBack pageId  argumentString     This will call the  RaisePostBackEvent  method in your code file with the  eventArgument  as the  argumentString  you passed from the JavaScript  Now  you can call any other event you like   P S  That is  underscore-underscore-doPostBack      And  there should be no space in that sequence    Somehow the WMD does not allow me to write to underscores followed by a character

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It is so easy for both scenarios  that is  synchronous asynchronous  if you want to trigger a server-side event handler  for example  Button s click event   For triggering an event handler of a control  If you added a ScriptManager on your page already then skip step 1    Add the following in your page client script section     lt   CDATA  var theForm   document forms  form1    if   theForm        theForm   document form1    function   doPostBack eventTarget  eventArgument        if   theForm onsubmit     theForm onsubmit      false             theForm   EVENTTARGET value   eventTarget          theForm   EVENTARGUMENT value   eventArgument          theForm submit                 gt     Write you server side event handler for your control  protected void btnSayHello Click object sender  EventArgs e         Label1 Text    Hello World        Add a client function to call the server side event handler  function SayHello               doPostBack  btnSayHello             Replace the  btnSayHello  in code above with your control s client id   By doing so  if your control is inside an update panel  the page will not refresh  That is so easy   One other thing to say is that  Be careful with client id  because it depends on you ID-generation policy defined with the ClientIDMode property

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