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:
Approach
- The function starts by setting the initial opacity of all images to 1 and initializing variables for tracking the topmost image (
top
) and the current image index (cur
). - It then sets up an interval using
setInterval
to call thechangeImage
function every 3 seconds. - The
changeImage
function transitions from one image to the next by adjusting the z-index of the current and next images. It uses thetransition
function to gradually decrease the opacity of the current image. - The
transition
function returns a promise, ensuring that the program waits for the opacity transition to complete before executing the next steps. - Inside
transition
, a separatesetInterval
is used to decrease the opacity of the current image until it reaches 0. Once the opacity is 0, the interval is cleared, and the promise is resolved.
Example: below is the implementation of above above-explained approach.
javascript
startImageTransition(); function startImageTransition() { // images stores list of all images of // class test. This is the list of images // that we are going to iterate let images = document.getElementsByClassName( "test" ); // Set opacity of all images to 1 for (let i = 0; i < images.length; ++i) { images[i].style.opacity = 1; } // Top stores the z-index of top most image let 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*/ let 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 let 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 let del = 0.01; // id stores ID of setInterval // this ID will be used later // to clear/stop setInterval // after we are done changing opacity let 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(); } } }) } } |
HTML
<!DOCTYPE html> < html > < head > < meta charset = "utf-8" /> < title > Change Image Dynamically when User Scrolls </ title > </ head > < body > < h1 >w3wiki</ h1 > < b >A Computer Science Portal for Beginner</ b > < div id = "scroll-image" > < img src = "https://media.w3wiki.net/wp-content/uploads/20200318142245/CSS8.png" class = "test" /> < img src = "https://media.w3wiki.net/wp-content/uploads/20200318142309/php7.png" class = "test" /> < img src = "https://media.w3wiki.net/wp-content/uploads/20200318142254/html9.png" class = "test" /> </ div > </ body > </ html > |
CSS
body { text-align : center ; } h 1 { color : green ; } img { position : absolute ; left : 400px ; } |
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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