html css javascript, Is it possible to execute a script before a webpage finishes loading?

My current setup is similar to a lightbox feature, but I'm facing an issue where the script waits for the entire webpage to load before running. Is there a way to ensure that my script runs first without waiting for the webpage to fully load?

CSS:

#overlay {
    display:none;    
    position:fixed;  
    left:0px;        
    top:0px;         
    width:100%;      
    height:100%;     
    background-image:url(gray.png); 
    z-index:99999;   
}

#popup {
    display:none;
    position:fixed;       
    width:500px; 
    margin-left:400px;
    margin-right:300px; 
    top:15%;   
    height:auto;
    background-color:white;
    z-index:100000;     
    border-radius: 3px;
    box-shadow: 0px 0px 0px 12px rgba(0,0,0,0.3);  
}

HTML:

<script type="text/javascript">
window.onload = function() {
        var overlay = document.getElementById("overlay");
        var popup = document.getElementById("popup");
        overlay.style.display = "block";
        popup.style.display = "block";

        document.getElementById("CloseBtn").onclick = function(){
        var overlay = document.getElementById("overlay");
        var popup = document.getElementById("popup");
        overlay.style.display = "none";
        popup.style.display = "none";      
  }
};
</script>

<div id="overlay"></div>
<div id="popup">

blah blah blah
javascripthtmlcss

Answer №1

This is the precise function of 

window.onload = function() { ... }
.

If you prefer it not to behave this way, simply do not instruct it to.

Answer №2

Implement window.onpaint.

<script type="text/javascript">
    window.onpaint = function() {
      // Perform actions
      }
    };
</script>

Remember, avoid using DOM elements inside the script.

Answer №3

To ensure the script runs properly, place it at the bottom of your HTML file just before the closing </body> tag without using window.onload:

<script type="text/javascript">
var modal = document.getElementById("modal");
var content = document.getElementById("content");
modal.style.display = "block";
content.style.display = "block";
// ...
</script>
</body>
</html>

Answer №4

I attempted to eliminate the use of window.onload without success. Could someone help me confirm if my bracket placement is correct in the code snippet below?

 <script type="text/javascript">
        var overlay = document.getElementById("overlay"); 
        var popup = document.getElementById("popup");
        overlay.style.display = "block";
        popup.style.display = "block";

        document.getElementById("CloseBtn").onclick = function(){
        var overlay = document.getElementById("overlay");
        var popup = document.getElementById("popup");
        overlay.style.display = "none";
        popup.style.display = "none";      
}
};
</script>

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