How to detect/track postback in javascript?

Question

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

Answer 1

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.

Answer 2

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') == 'True';
}

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

Answer 3

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>

Answer 4

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 %>;
}