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

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 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')