How can I check for IsPostBack in JavaScript? [duplicate]

Question

I need to run a JavaScript function onLoad(), but only do it if the page loaded the first time (i.e. is not the result of a postback).

Basically, I need to check for IsPostBack in JavaScript.

Thank you.

Answer 1

Server-side, write:

if(IsPostBack) {    // NOTE: the following uses an overload of RegisterClientScriptBlock()     // that will surround our string with the needed script tags     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 your thing } 

---

You don't really need to set the variable otherwise, like Jonathan's solution. The client-side if statement will work fine because the "isPostBack" variable will be undefined, which evaluates as false in that if statement.

Answer 2

There is an even easier way that does not involve writing anything in the code behind: Just add this line to your javascript:

if(<%=(Not Page.IsPostBack).ToString().ToLower()%>){//Your JavaScript goodies here} 

or

if(<%=(Page.IsPostBack).ToString().ToLower()%>){//Your JavaScript goodies here}