How to detect/track postback in javascript?

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

o.k.w

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.

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.

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 %>;
}

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')

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>

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");
});

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.

Here is solution using jQuery:

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

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
}

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;
}

来源：https://stackoverflow.com/questions/1857606/how-to-detect-track-postback-in-javascript

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