Javascript before onload?

by

If you put Javascript statements (rather than function definitions) inside a <script> tag, they will be executed during page loading – before the onLoad event is fired.

 <html>
 <body>
   <h2>First header</h2>
   <script type="text/javascript">
     alert("Hi, I am here"); 
     document.write("<h3>This is Javascript generated</h3>");
   </script>
   <h2>Second header</h2>
 </body>
 </html>

The caveat is that you cannot search for elements by ID because these element might not have been rendered yet, so your ability to change the page that way is limited.

Bottom line: possible, not recommended.

What I usually do in such situations is as follows:

  • Make the parts of the page that may change invisible (via style="visibility:hidden;");
  • Make onLoad run a Javascript code that changes the page and then sets the visibility of the said parts to visibility:visible.

More Related Contents:

  1. Checkbox hidden on body load [closed]
  2. How to run a function when the page is loaded?
  3. iFrame src change event detection?
  4. How do I call a JavaScript function on page load?
  5. Trying to fire the onload event on script tag
  6. Execute write on doc: It isn’t possible to write into a document from an asynchronously-loaded external script unless it is explicitly opened.
  7. Javascript – How to detect if document has loaded (IE 7/Firefox 3)
  8. How to run function in AngularJS controller on document ready?
  9. ‘onload’ handler for ‘script’ tag in internet explorer
  10. Javascript read file without using input
  11. Best practice for using window.onload
  12. Cannot set property ‘innerHTML’ of null
  13. Attach a body onload event with JS
  14. AngularJS – Image “onload” event
  15. What html tags support the onload/onerror javascript event attributes?
  16. Difference between onload() and $.ready?
  17. Recall Tampermonkey script when page location changes
  18. javascript – document.write error?
  19. iFrame onload JavaScript event
  20. When to use “window.onload”?
  21. Async-loaded scripts with DOMContentLoaded or load event handlers not being called?
  22. Is there a way to have an onload callback after changing window.location.href?
  23. Is bubbling available for image load events?
  24. Find list of strings that matches a pattern that start with a special character « and end with a special character »
  25. How can I hide the Android keyboard using JavaScript?
  26. AngularJS sorting by property
  27. Deprecation warning in Moment.js – Not in a recognized ISO format
  28. Combining two arrays to form a javascript object
  29. how to auto select an input field and the text in it on page load
  30. Can I do SendKeys in Javascript?

Leave a Comment