Image Transition with Fading Effect using JavaScript
In this article, we are given some images and the task is the create a slow transition from one image to another using Javascript.
Prerequisite: In this article, we will use the following JavaScript methods.
Approach: Given some images and the task is to change the images after regular intervals with a fading or dissolving effect. To change the image at regular intervals using the setInterval() method. Keep the images on top of each other and keep moving the topmost image to the bottom by changing its z-index at regular intervals.
To make the image transition with a fading effect we use the asynchronous function. Inside the asynchronous function, use another setInterval() method to slowly decrease the opacity of the topmost image till opacity becomes 0. By doing this, the topmost image will appear to fade away slowly. Once, the topmost image is completely faded away, move it to the bottom-most position and store the new top image index.
Example:
HTML
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title> Change Image Dynamically when User Scrolls </title> </head> <body> <h1>GeeksforGeeks</h1> <b>A Computer Science Portal for Geeks</b> <div id="scroll-image"> <img src= class="test" /> <img src= class="test" /> <img src= class="test" /> </div> </body> </html> |
CSS
body { text-align: center; } h1 { color: green; } img { position: absolute; left: 400px; } |
javascript
<script> startImageTransition(); function startImageTransition() { // images stores list of all images of // class test. This is the list of images // that we are going to iterate var images = document.getElementsByClassName("test"); // Set opacity of all images to 1 for (var i = 0; i < images.length; ++i) { images[i].style.opacity = 1; } // Top stores the z-index of top most image var top = 1; // cur stores the index of the image currently // on top images list contain images in the // same order they appear in HTML code /* The tag with class test which appears last will appear on top of all the images thus, cur is set to last index of images list*/ var cur = images.length - 1; // Call changeImage function every 3 second // changeImage function changes the image setInterval(changeImage, 3000); // Function to transitions from one image to other async function changeImage() { // Stores index of next image var nextImage = (1 + cur) % images.length; // First set the z-index of current image to top+1 // then set the z-index of nextImage to top /* Doing this make sure that the image below the current image is nextImage*/ // if this is not done then during transition // we might see some other image appearing // when we change opacity of the current image images[cur].style.zIndex = top + 1; images[nextImage].style.zIndex = top; // await is used to make sure // the program waits till transition() // is completed // before executing the next line of code await transition(); // Now, the transition function is completed // thus, we can say that the opacity of the // current image is now 0 // Set the z-index of current image to top images[cur].style.zIndex = top; // Set the z-index of nextImage to top+1 images[nextImage].style.zIndex = top + 1; // Increment top top = top + 1; // Change opacity of current image back to 1 // since zIndex of current is less than zIndex // of nextImage /* changing it's opacity back to 1 will not make the image appear again*/ images[cur].style.opacity = 1; // Set cur to nextImage cur = nextImage; } /* This function changes the opacity of current image at regular intervals*/ function transition() { return new Promise(function (resolve, reject) { // del is the value by which opacity is // decreased every interval var del = 0.01; // id stores ID of setInterval // this ID will be used later // to clear/stop setInterval // after we are done changing opacity var id = setInterval(changeOpacity, 10); // changeOpacity() decreasing opacity of // current image by del // when opacity reaches to 0, we stops/clears // the setInterval and resolve the function function changeOpacity() { images[cur].style.opacity -= del; if (images[cur].style.opacity <= 0) { clearInterval(id); resolve(); } } }) } } </script> |
Output: Click here to check the live output.
Note: The time interval at which images are changing should be greater than the time it takes to make the opacity of the image less than or equals to 0.
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