Calling JavaScript Function From CodeBehind

Question

Can someone provide good examples of calling a JavaScript function From CodeBehind and Vice-versa

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If you need to send a value as a parameter   string jsFunc    myFunc     MyBackValue        ScriptManager RegisterStartupScript this Page  Page GetType     myJsFn   jsFunc  true

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Thank  Liko   just add a comment to his answer   string jsFunc    myFunc     MyBackValue        ScriptManager RegisterStartupScript this Page  Page GetType     myJsFn   jsFunc  true     Added single quotes     to variable  otherwise it will give error message   string jsFunc    myFunc      MyBackValue

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ScriptManager RegisterStartupScript this  this Page GetType    updatePanel1Script    javascript ConfirmExecute    true  gt

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Since I couldn t find a solution that was code behind  which includes trying the ClientScript and ScriptManager like mutanic and Orlando Herrera said in this question  they both somehow failed   I ll offer a front-end solution that utilizes button clicks to others if they re in the same position as me  This worked for me   HTML Markup    lt asp button ID  myButton  runat  server  Text  Submit  OnClientClick  return myFunction     gt  lt  asp button gt    JavaScript   function myFunction            Your JavaScript code     return false      I am simply using an ASP NET button which utilizes the OnClientClick property  which fires client-side scripting functions  that being JavaScript  The key things to note here are the uses of the return keyword in the function call and in the function itself  I ve read docs that don t use return but still get the button click to work - somehow it didn t work for me  The return false  statement in the function specifies a postback should NOT happen  You could also use that statement in the OnClientClick property  OnClientClick  myFunction   return false

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ScriptManager RegisterStartupScript Page  GetType     JavaFunction    AlertError      true     using your function is enough

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You can use literal   this Controls Add new LiteralControl   lt script type  text javascript  gt myFunction    lt  script gt

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You can expose C  methods on codebehind pages to be callable via JavaScript by using the ScriptMethod attribute   You cannot call JavaScript from a CodeBehind - that code exists solely on the client

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Another thing you could do is to create a session variable that gets set in the code behind and then check the state of that variable and then run your javascript  The good thing is this will allow you to run your script right where you want to instead of having to figure out if you want it to run in the DOM or globally    Something like this  Code behind   Session  newuser      false     In javascript  var newuser     lt   Session  newuser    gt     if  newuser     yes        startTutorial

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You cannot  Codebehind is running on the server while JavaScript is running on the client   However  you can add  lt script type  text javascript  gt someFunction    lt  script gt  to your output and thus cause the JS function to be called when the browser is parsing your markup

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Working Example      lt    Page Title    Language  C   MasterPageFile    MasterPage2 Master  AutoEventWireup  true  CodeBehind  History aspx cs  Inherits  NAMESPACE Web History1    gt    lt asp Content ID  Content1  ContentPlaceHolderID  head  runat  Server  gt       lt    Register Assembly  AjaxControlToolkit  Namespace  AjaxControlToolkit  TagPrefix  ajax    gt      lt script type  text javascript  src  https   ajax googleapis com ajax libs jquery 1 8 2 jquery min js  gt  lt  script gt             lt script type  text javascript  gt               function helloFromCodeBehind                     alert  hello                             lt  script gt    lt  asp Content gt    lt asp Content ID  Content2  ContentPlaceHolderID  ContentPlaceHolder1  runat  Server  gt     lt div id  container    gt  lt  div gt    lt  asp Content gt    Code Behind  using System  using System Collections Generic  using System Linq  using System Web  using System Web UI  using System Web UI WebControls   namespace NAMESPACE Web       public partial class History1   System Web UI Page               protected void Page Load object sender  EventArgs e                         ScriptManager RegisterStartupScript this  GetType     displayalertmessage    helloFromCodeBehind     true                        Possible pitfalls -    Code and HTML might not be in same namespace CodeBehind  History aspx cs  is pointing to wrong page JS function is having some error

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I ve been noticing a lot of the answers here are using ScriptManager RegisterStartupScript and if you are going to do that  that isn t the right way to do it   The right way is to use ScriptManager RegisterScriptBlock  my list of args here     The reason being is you should only be using RegisterStartupScript when your page loads  hence the name RegisterStartupScript    In VB NET   ScriptManager RegisterClientScriptBlock Page  GetType String    myScriptName    key    myFunctionName  someJavascriptObject     True    in C     ScriptManager RegisterClientScriptBlock Page  typeof string    myScriptName    key    myFunctionName  someJavascriptObject     true     Of course  I hope it goes without saying that you need to replace key with your key identifier and should probably move all of this into a sub function method and pass in key and someJavascriptObject  if your javascript method requires that your arg is a javascript object    MSDN docs   https   msdn microsoft com en-us library bb338357 v vs 110  aspx

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C  to JavaScript  you can register script block to run on page like following   ClientScript RegisterStartupScript GetType    hwa   alert  Hello World     true     replace alert   part with your function name   For calling C  method from JavaScript you can use ScriptManager or jQuery  I personally use jQuery  You need to decorate the method that you want to call from JavaScript with WebMethod attribute  For more information regarding calling C  method  called PageMethod  from jQuery you can refer to Dave Ward s post

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You can t call a Javascript function from the CodeBehind  because the CodeBehind file contains the code that executes server side on the web server  Javascript code executes in the web browser on the client side

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this works for me   object Json Object maintainerService Convert To JSON Jobitem   ScriptManager RegisterClientScriptBlock this GetType     Javascript    SelectedJobsMaintainer   Json Object       true

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You can not do this directly  In standard WebForms JavaScript is interpreted by browser and C  by server  What you can do to call a method from server using JavaScript is    Use WebMethod as attribute in target methods   Add ScriptManager setting EnablePageMethods as true  Add JavaScript code to call the methods through the object PageMethods    Like this   Step 1  public partial class Products   System Web UI Page          System Web Services WebMethod          System Web Script Services ScriptMethod         public static List lt Product gt  GetProducts int cateogryID                    Put your logic here to get the Product list          Step 2  Adding a ScriptManager on the Page   lt asp ScriptManager ID  ScriptManager1  runat  server  EnablePageMethods  true    gt    Step 3  Calling the method using JavaScript  function GetProductsByCategoryID categoryID        PageMethods GetProducts categoryID  OnGetProductsComplete       Take a look at this link   To call a JavaScript function from server you can use RegisterStartupScript   ClientScript RegisterStartupScript GetType    id   callMyJSFunction    true

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This is how I ve done it   HTML markup showing a label and button control is as follows    lt body gt      lt form id  form1  runat  server  gt      lt div gt        lt asp Label ID  lblJavaScript  runat  server  Text    gt  lt  asp Label gt        lt asp Button ID  btnShowDialogue  runat  server  Text  Show Dialogue    gt      lt  div gt      lt  form gt    lt  body gt    JavaScript function is here    lt head runat  server  gt      lt title gt Calling javascript function from code behind example lt  title gt      lt script type  text javascript  gt       function showDialogue            alert  this dialogue has been invoked through codebehind                lt  script gt    lt  head gt    Code behind to trigger the JavaScript function is here   lblJavaScript Text     lt script type  text javascript  gt showDialogue    lt  script gt

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Calling a JavaScript function from code behind  Step 1 Add your Javascript code   lt script type  text javascript  language  javascript  gt      function Func             alert  hello           lt  script gt    Step 2 Add 1 Script Manager in your webForm and Add 1 button too  Step 3 Add this code in your button click event   ScriptManager RegisterStartupScript this Page  Page GetType     text    Func     true

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Try This in Code Behind and it will worked 100   Write this line of code in you Code Behind file   string script    window onload   function     YourJavaScriptFunctionName         ClientScript RegisterStartupScript this GetType     YourJavaScriptFunctionName   script  true     And this is the web form page   lt script type  text javascript  gt      function YourJavaScriptFunctionName             alert  Test           lt  script gt

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I used ScriptManager in Code Behind and it worked fine   ScriptManager RegisterStartupScript UpdatePanel1  UpdatePanel1 GetType     CallMyFunction    confirm     true     If you are using UpdatePanel in ASP Frontend  Then  enter UpdatePanel name and  function name  defined with script tags

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IIRC Code Behind is compiled serverside and javascript is interpreted client side  This means there is no direct link between the two   What you can do on the other hand is have the client and server communicate through a nifty tool called AJAX  http   en wikipedia org wiki Asynchronous JavaScript and XML

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You may try this    Page ClientScript RegisterStartupScript this GetType    CallMyFunction   MyFunction    true

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