How to make JavaScript execute after page load

Question

I m executing an external script  using a  lt script gt  inside  lt head gt    Now since the script executes before the page has loaded  I can t access the  lt body gt   among other things  I d like to execute some JavaScript after the document has been  loaded   HTML fully downloaded and in-RAM   Are there any events that I can hook onto when my script executes  that will get triggered on page load

User · Answer

Using the YUI library  I love it    YAHOO util Event onDOMReady function          your code       Portable and beautiful  However  if you don t use YUI for other stuff  see its doc  I would say that it s not worth to use it   N B    to use this code you need to import 2 scripts   lt script type  text javascript  src  http   yui yahooapis com 2 7 0 build yahoo yahoo-min js   gt  lt  script gt   lt script type  text javascript  src  http   yui yahooapis com 2 7 0 build event event-min js   gt  lt  script gt

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My advise use asnyc attribute for script tag thats help you to load the external scripts after page load    lt script type  text javascript  src  a js  async gt  lt  script gt   lt script type  text javascript  src  b js  async gt  lt  script gt

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There is a very good documentation on How to detect if document has loaded using Javascript or Jquery   Using the native Javascript this can be achieved  if  document readyState      complete      init         This can also be done inside the interval  var interval   setInterval function         if document readyState      complete             clearInterval interval           init                 100     Eg By Mozilla  switch  document readyState      case  loading          The document is still loading      break    case  interactive          The document has finished loading  We can now access the DOM elements      var span   document createElement  span        span textContent    A  lt span gt  element        document body appendChild span       break    case  complete          The page is fully loaded      console log  Page is loaded completely        break      Using Jquery To check only if DOM is ready     A    document   ready   block     document   ready function         console log   ready            To check if all resources are loaded use window load      window   load function             console log   window loaded

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Comparison  In below snippet I collect choosen methods and show their sequence  Remarks   the document onload  X  is not supported by any modern browser  event is never fired  if you use  lt body onload  bodyOnLoad    gt   F  and at the same time window onload  E  then only first one will be executed  because it override second one  event handler given in  lt body onload       gt   F   is wrapped by additional onload function document onreadystatechange  D  not override document  addEventListener  readystatechange       C  probably cecasue onXYZevent-like methods are independent than addEventListener queues  which allows add multiple listeners   Probably nothing happens between execution this two handlers  all scripts write their timestamp in console - but scripts which also have access to div write their timestamps also in body  click  Full Page  link after script execution to see it   solutions readystatechange  C D  are executed multiple times by browser but for different document states    loading - the document is loading  no fired in snippet  interactive - the document is parsed  fired before DOMContentLoaded complete - the document and resources are loaded  fired before body window onload     x000D   x000D   lt html gt  x000D   x000D   lt head gt  x000D     lt script gt  x000D         solution A x000D      console log   timestamp    Date now     A  Head script    x000D       x000D         solution B x000D      document addEventListener  DOMContentLoaded        gt    x000D        print   timestamp    Date now     B  DOMContentLoaded    x000D          x000D   x000D         solution C x000D      document addEventListener  readystatechange        gt    x000D        print   timestamp    Date now     C  ReadyState    document readyState     x000D          x000D      x000D         solution D x000D      document onreadystatechange   s  gt   print   timestamp    Date now     D  document onreadystatechange ReadyState    document readyState      x000D       x000D         solution E  never executed  x000D      window onload        gt    x000D        print  E   lt body onload       gt  override this handler    x000D         x000D   x000D         solution F x000D      function bodyOnLoad     x000D        print   timestamp    Date now     F   lt body onload       gt           x000D        infoAboutOnLoad       additional info x000D        x000D       x000D         solution X x000D      document onload        gt   print  document onload is never fired     x000D   x000D   x000D   x000D         HELPERS x000D   x000D      function print txt     x000D        console log txt   x000D        if mydiv  mydiv innerHTML    txt replace   lt     amp lt    replace   gt     amp gt        lt br gt    x000D        x000D       x000D      function infoAboutOnLoad     x000D        console log  window onload  after  override         document body onload  replace   s  g        x000D        console log  body onload  window onload -- gt    document body onload  window onload     x000D        x000D               x000D      console log  window onload  before override         document body onload  replace   s  g        x000D   x000D     lt  script gt  x000D   lt  head gt  x000D   x000D   lt body onload  bodyOnLoad    gt  x000D     lt div id  mydiv  gt  lt  div gt  x000D   x000D     lt  -- this script must te at the bottom of  lt body gt  -- gt  x000D     lt script gt  x000D         solution G x000D      print   timestamp    Date now     G   lt body gt  bottom script    x000D     lt  script gt  x000D   lt  body gt  x000D   x000D   lt  html gt  x000D   x000D   x000D

User · Answer

lt script type  text javascript  gt    function downloadJSAtOnload        var element   document createElement  script       element src    defer js      document body appendChild element         if  window addEventListener     window addEventListener  load   downloadJSAtOnload  false     else if  window attachEvent     window attachEvent  onload   downloadJSAtOnload     else window onload   downloadJSAtOnload   lt  script gt    http   www feedthebot com pagespeed defer-loading-javascript html

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document onreadystatechange   function         if document readyState      complete               code here              look here  http   msdn microsoft com en-us library ie ms536957 v vs 85  aspx

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JavaScript  document addEventListener  readystatechange   event   gt             When HTML DOM elements are ready      if  event target readyState      interactive         does same as     addEventListener  DOMContentLoaded            alert  hi 1                  When window loaded   external resources are loaded too-  css   src   etc          if  event target readyState      complete             alert  hi 2                same for jQuery     document  ready function         same as    function           alert  hi 1           window  load function          alert  hi 2              NOTE  - Don t use the below markup   because it overwrites other same-kind declarations      document onreadystatechange

User · Answer

These solutions will work    lt body onload  script     gt    or  document onload   function       or even  window onload   function       Note that the last option is a better way to go since it is unobstrusive and is considered more standard

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x000D   x000D   lt script type  text javascript  gt  x000D    window  bind  load   function      x000D   x000D     your javascript event here x000D   x000D      x000D   lt  script gt  x000D   x000D   x000D

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Working Fiddle on  lt body onload  myFunction    gt    lt  DOCTYPE html gt   lt html gt    lt head gt     lt script type  text javascript  gt     function myFunction        alert  Page is loaded            lt  script gt    lt  head gt     lt body onload  myFunction    gt     lt h1 gt Hello World  lt  h1 gt    lt  body gt       lt  html gt

User · Answer

lt body onload  myFunction    gt    This code works well   But window onload method has various dependencies  So it may not work all the time

User · Answer

Just define  lt body onload  aFunction    gt  that will be called after the page has been loaded  Your code in the script is than enclosed by aFunction

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In simple terms just use  quot defer quot  in the script tag

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Here s a script based on deferred js loading after the page is loaded    lt script type  text javascript  gt    function downloadJSAtOnload           var element   document createElement  script          element src    deferredfunctions js         document body appendChild element          if  window addEventListener        window addEventListener  load   downloadJSAtOnload  false     else if  window attachEvent        window attachEvent  onload   downloadJSAtOnload     else window onload   downloadJSAtOnload   lt  script gt    Where do I place this      Paste code in your HTML just before the  lt  body gt  tag  near the bottom of your HTML file      What does it do      This code says wait for the entire document to load  then load the    external file deferredfunctions js    Here s an example of the above code - Defer Rendering of JS  I wrote this based on defered loading of javascript pagespeed google concept and also sourced from this article Defer loading javascript

User · Answer

You can put a  onload  attribute inside the body      lt body onload  myFunction    gt       Or if you are using jQuery  you can do     document  ready function      code here        or     window  load function      code here        I hope it answer your question   Note that the   window  load will execute after the document is rendered on your page

User · Answer

Look at hooking document onload or in jQuery   document  load

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If the scripts are loaded within the  lt head gt  of the document  then it s possible use the defer attribute in script tag   Example    lt script src  demo defer js  defer gt  lt  script gt    From https   developer mozilla org      defer      This Boolean attribute is set to indicate to a browser that the script   is meant to be executed after the document has been parsed  but before   firing DOMContentLoaded        This attribute must not be used if the src   attribute is absent  i e  for inline scripts   in this case it would   have no effect       To achieve a similar effect for dynamically inserted scripts use   async false instead  Scripts with the defer attribute will execute in   the order in which they appear in the document

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Reasonably portable  non-framework way of having your script set a function to run at load time   if window attachEvent        window attachEvent  onload   yourFunctionName     else       if window onload            var curronload   window onload          var newonload   function evt                curronload evt               yourFunctionName evt                      window onload   newonload        else           window onload   yourFunctionName

User · Answer

As Daniel says  you could use document onload   The various javascript frameworks hwoever  jQuery  Mootools  etc   use a custom event  domready   which I guess must be more effective   If you re developing with javascript  I d highly recommend exploiting a framework  they massively increase your productivity

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Keep in mind that loading the page has more than one stage  Btw  this is pure JavaScript   DOMContentLoaded   This event is fired when the initial HTML document has been completely loaded and parsed  without waiting for stylesheets  images  and subframes to finish loading  At this stage you could programmatically optimize loading of images and css based on user device or bandwidth speed   Executes after DOM is loaded  before img and css     document addEventListener  DOMContentLoaded   function                        Note  Synchronous JavaScript pauses parsing of the DOM    If you want the DOM to get parsed as fast as possible after the user requested the page  you could turn your JavaScript asynchronous and optimize loading of stylesheets    load   A very different event  load  should only be used to detect a fully-loaded page  It is an incredibly popular mistake to use load where DOMContentLoaded would be much more appropriate  so be cautious   Exectues after everything is loaded and parsed    window addEventListener  load   function                        MDN Resources   https   developer mozilla org en-US docs Web Events DOMContentLoaded https   developer mozilla org en-US docs Web Events load  MDN list of all events   https   developer mozilla org en-US docs Web Events

User · Answer

I find sometimes on more complex pages that not all the elements have loaded by the time window onload is fired  If that s the case  add setTimeout before your function to delay is a moment  It s not elegant but it s a simple hack that renders well   window onload   function    doSomethingCool         becomes     window onload   function    setTimeout  function    doSomethingCool       1000

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Use this code with jQuery library  this would work perfectly fine     window  bind  load   function            your javascript event

User · Answer

If you are using jQuery      function             is equivalent to     document  ready function          or another short hand       ready function          See What event does JQuery  function   fire on  and https   api jquery com ready

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window  on  load   function               ready   works best for me     document  ready function               load   will work  but it won t wait till the page is loaded   jQuery window  load function                Doesn t work for me  breaks the next-to inline script  I am also using jQuery 3 2 1 along with some other jQuery forks   To hide my websites loading overlay  I use the following    lt script gt    window  on  load   function        loading-page   delay 3000  fadeOut 250        lt  script gt

[javascript] How to make JavaScript execute after page load?

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