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

by

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.

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