Page loading techniques for window.onload_javascript techniques

After testing the two pieces of code separately, it was found that window.onload without brackets showed the correct effect after the page was loaded. I think window.onload is also equivalent to a trigger event. If the function has parentheses, the function will be executed directly first, and then the body will be loaded. Without parentheses, it is equivalent to assigning a function as a variable to window.onload and not loading it immediately.

Code 1:

<div id="div1"> </div>
[Ctrl A Select all Note: If you need to introduce external Js, you need to refresh to execute

]


Code 2:

<div id="div1"> </div>
[Ctrl A select all Note:

If you need to introduce external Js, you need to refresh to execute <script> window.onload = doIt(); function doIt() { var oDiv = document.getElementById("div1"); alert (oDiv); } </script>]<script> window.onload = doIt; function doIt() { var oDiv = document.getElementById("div1"); alert (oDiv); } </script>