How can I check for IsPostBack in JavaScript

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

User · Answer

hi try the following      function pageLoad  sender  args     alert  args  isPartialLoad        the result is a Boolean

User · Answer

Create a global variable in and apply the value   lt script gt         var isPostBack    lt   Convert ToString Page IsPostBack  ToLower    gt    lt  script gt    Then you can reference it from elsewhere

User · Answer

Lots of options here   For a pure JS solution  have your page submit to itself  but with additional URL parameter  mypage html postback true  - you can then get the page url with window location href  and parse that using a split or regex to look for your variable   The much easier one  assuming you sending back to some sort of scripting language to proces the page  php perl asp cf et  al   is to have them echo a line of javascript in the page setting a variable    lt html gt    lt  php if    POST  myVar            postback     echo   lt script gt var postingBack   true  lt  script gt          Do other processing   else       echo   lt script gt var postingBack   false  lt  script gt        gt   lt script gt  function myLoader          if  postingBack    false                Do stuff             lt body onLoad  myLoader     gt

User · Answer

You can create a hidden textbox with a value of 0  Put the onLoad   code in a if block that checks to make sure the hidden text box value is 0  if it is execute the code and set the textbox value to 1

User · Answer

The solution didn t work for me  I had to adapt it   protected void Page Load object sender  EventArgs e        string script      if  IsPostBack                script    var isPostBack   true              else               script    var isPostBack   false              Page ClientScript RegisterStartupScript GetType     IsPostBack   script  true       Hope this helps

User · Answer

Try this  in this JS we can check if it is post back or not and accordingly do operations in the respective loops          window onload   isPostBack       function isPostBack              if   document getElementById  clientSideIsPostBack                  return false                     if  document getElementById  clientSideIsPostBack   value     Y                        DO ALL POST BACK RELATED WORK HERE                 return true                    else                      DO ALL INITIAL LOAD RELATED WORK HERE                 return false

User · Answer

You could put a hidden input on the page  and after the page loads  give it a value   Then you can check that field  if it was in the post data  it s a postback  otherwise it is not   There were two solutions that used server side code  ASP NET specific  posted as responses   I think it is worth pointing out that this solution is technology agnostic since it uses client side features only  which are available in all major browsers

User · Answer

Here is one way  put this in Page Load    if  this IsPostBack        Page ClientScript RegisterStartupScript this GetType    PostbackKey    lt script type  text javascript  gt var isPostBack   true  lt  script gt         Then just check that variable in the JS

User · Answer

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

User · Answer

There is an even easier way that does not involve writing anything in the code behind  Just add this line to your javascript   if  lt    Not Page IsPostBack  ToString   ToLower    gt     Your JavaScript goodies here    or  if  lt    Page IsPostBack  ToString   ToLower    gt     Your JavaScript goodies here

[asp.net] How can I check for IsPostBack in JavaScript?

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