CODEWITHSUNDEEP
asp.netjavascriptpostback
Subrat
Subrat

Reputation: 901

How to detect/track postback in javascript?

How to detect/track/check postback in javascript(e.g in asp.net Page.isPostBack())? Any suggestion?

Upvotes: 27

Views: 88842

Answers (11)

Sir Asks a Lot
Sir Asks a Lot

Reputation: 19

This is a simple JS way to determine the status of IsPostBack that I just got working in the Body of my ASPX page; needed to cause a PostBack during PageLoad for a project.

    <script type="text/javascript">
        if ('False' === '<%= Page.IsPostBack.ToString()%>') 
        {
            __doPostBack();
        }
    </script>

Upvotes: 0

Olymp Medco
Olymp Medco

Reputation: 1

This should work for ASP.Net pages without relying on a backend supplied variable/control:

function isPostBack(frmID) {
    var eventtarget = "";
    var eventargument = "";

    if (!!frmID) {
        if (document.forms.length == 0) return false;

        sForm = document.forms[0];
    }
    else {
        sForm = document.getElementById(frmID);

        if (!sForm) return false;
    }

    if (sForm.__EVENTTARGET) eventtarget = sForm.__EVENTTARGET.value;
    else return false;

    if (sForm.__EVENTARGUMENT) eventargument = sForm.__EVENTARGUMENT.value;
    else return false;

    if (eventtarget != "" || eventargument != "") return true;
    else return false;
}

Upvotes: 0

Lequoa
Lequoa

Reputation: 11

on Page_Load on your server-side : The following uses an overload of RegisterClientScriptBlock() that will surround our string with the needed script tags

Server-Side

if (Page.IsPostBack){
   ClientScript.RegisterClientScriptBlock(GetType(),
            "IsPostBack", "var isPostBack = true;", true);
}

Then in your script which runs for the onLoad, check for the existence of that variable.

if (isPostBack){
   //do something here
}

Upvotes: 0

user4640122
user4640122

Reputation: 51

I have a solution that worked for me.

// Postback catch
var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_endRequest(function (s, e) {
    alert("post back");
});

Upvotes: 5

o.k.w
o.k.w

Reputation: 25790

ASPX:

<input type="hidden" id="_ispostback" value="<%=Page.IsPostBack.ToString()%>" />

Client-side Script:

function isPostBack() { //function to check if page is a postback-ed one
  return document.getElementById('_ispostback').value == 'True';
}

PS: I have not tested it but I've done somthing similar before and it works.

Upvotes: 42

Mishami
Mishami

Reputation: 470

Here is solution using jQuery:

$("a[href^='javascript:__doPostBack']").click(function () {
    alert('ok');
});

Upvotes: -1

zzzzBov
zzzzBov

Reputation: 179046

As JavaScript shouldn't be written with server-side code, and injecting new elements into the page seems like overkill, it seems to me that the simplest solution is to add [datat-*] attributes to the <head> element:

In Page_Load: 
Page.Header.Attributes["data-is-postback"] IsPostBack ? "true" : "false";

This can then be accessed as:

jQuery: 
$('head').data('isPostback');
Vanilla JS: 
document.head.getAttribute('data-is-postback') === 'true';

Of course, if you treat the [data-is-postback] attribute as a boolean attribute, you could alternatively use:

In Page_Load: 
if (IsPostBack)
{
    Page.Header.Attributes.Add("data-is-postback", "");
}
else
{
    Page.Header.Attributes.Remove("data-is-postback");
}
jQuery: 
$('head').is('[data-is-postback]');
Vanilla JS: 
document.head.hasAttribute('data-is-postback')

Upvotes: 6

Daniel
Daniel

Reputation: 3131

In some cases, you may want to check for postback without any server-side code. For example, in SharePoint, you cannot have code blocks in SharePoint Designer pages, so you can't use any solution that requires <%=something %>. Here is an alternative that involves no server-side code:

<script type="text/javascript">
 function isPostBack()
 {

  return document.referrer.indexOf(document.location.href) > -1;
 }

 if (isPostBack()){
document.write('<span style="color:red;">Your search returned no results.</span><br/>');
 }
 </script>

One caveat (or feature, depending on how you look at it), this will detect not just postbacks, but any instance where the page links to itself.

Upvotes: 22

RickNZ
RickNZ

Reputation: 18654

If you want to check whether the current page will be a postback if the user clicks on a submit button, you can check for the presence of ViewState:

<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="xxxxx" />

You can use something like document.getElementById("__VIEWSTATE") or the jQuery equivalent.

However, if you want to see whether the current page was generated in response to a postback, then you need to insert that data into the page on the server side first.

For example:

function isPostBack() {
  return <%= Page.IsPostBack %>;
}

Upvotes: 9

Brij
Brij

Reputation: 6122

See following:

<script type="text/javascript">

function invokeMeMaster() {

var chkPostBack = '<%= Page.IsPostBack ? "true" : "false" %>';

if (chkPostBack == 'false') {

alert('Only the first time');

}
}



window.onload = function() { invokeMeMaster(); };

</script>

Upvotes: 4

Robert Massaioli
Robert Massaioli

Reputation: 13477

You can only keep track of the postback if you are using AJAX requests or have a hidden field of some sort that the javascript reads on page load. Otherwise the page is regenerated and all POST data is lost; as you would expect and hope.

Upvotes: 0

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