In web development, it is very important to make sure that users only see content when it is visible to them. It is a crucial step for improving performance and user experience. One common task is determining whether a DOM element is visible in the current viewport (the part of the web page the user can see without scrolling. There are several methods to check this, like getBoundingClientRect() and IntersectionObserver API. But before proceeding with these methods, it’s important for us to understand more about the DOM and Viewport.
Table of Contents:
What is a DOM Element and the Viewport?
DOM Stands for Document Object Model, it is nothing but a tree-like structure that is prepared by your browser whenever you load a web page in your web browser. It is a way of representing the structure of an HTML document in JavaScript. A DOM element is just an HTML element in a webpage (like an image, button, text, etc.).
The viewport is the visible area of a webpage on your screen. In other words, you can say it’s the part of the webpage you can see without having to scroll.
Ways to Check if the DOM Element is Visible in the Current Viewport
Now you’re clear about the DOM elements and the viewport. Let’s learn about different methods that can be used to check whether the DOM element is visible in your viewport or not.
Method 1: Using the getBoundingClientRect() Method
This javascript method is very helpful for checking DOM element visibility in the current viewport. This method gives you the position of the element relative to the viewport (not the entire page). It helps in measuring the position of HTML elements precisely.
Example:
Output:
Explanation: This code uses the getBoundingClientRect() method to check if a DOM element is entirely visible within the viewport. When the button is clicked, it checks the element’s position and displays whether it is fully inside the visible area of the browser window.
This approach checks if the element is within the scrollable area or not. This method is easy to execute, but it’s not as accurate as the previous one.
Example:
Output:
Explanation: It checks the visibility of the DOM element using window.scrollY and window.innerHeight. When the page is scrolled, it triggers a visibility check and updates the status message. The target element's background color changes to green when it is visible and changes to blue when it is out of the viewport.
Method 3: Using IntersectionObserver API
This is a modern way to detect if an element is visible. It allows you to see the changes in the intersection of an element with the viewport. This method is more efficient to use as compared to the scroll event because it’s asynchronous and doesn’t continuously check during scrolling.
Example:
Output:
Explanation:
- First, an observer is created to monitor events.
- After that, when an element is visible in the viewport, then the message is shown “The element is visible in the viewport.” Otherwise, it shows “The element is not visible in the viewport”.
This method is highly efficient because it only shows results when the visibility changes, reducing unnecessary checks during scrolling.
Comparison Between All Methods
Here, is the comparison between all those ways that are available to check whether a DOM element is inside a viewport or not:
|
Feature |
getBoundingClientRect() | IntersectionObserver API | Scroll Events |
| How it works | Returns the element’s position & size relative to the viewport. | Parallelly observes when an element enters or exits the viewport. | It triggers an event whenever the user scrolls. |
| Performance | Medium | High | Low |
| Ease of use | Simple (Just call element.getBoundingClientRect() ) | Moderate (Requires setting up an observer) | Simple (Add a Scroll event listener) |
| Accuracy | Very Accurate | Very Accurate | inaccurate due to scroll lag |
| Use Cases | popups, and animations on viewport entry | Lazy loading images, infinite scrolling, viewport tracking, | Triggering actions on scroll (e.g., progress bars) |
Handling Errors While Checking Element Visibility
When you’re dealing with these methods, sometimes you get errors. Let’s see what those errors are and how you can resolve them:
1. Element Not Found (Null Reference Error)
Issue: You may get this error "Cannot read property 'getBoundingClientRect' of null" when trying to access an element that doesn't exist in the DOM.
Example:
const element = document.getElementById('nonExistentingElement');
const rect = element.getBoundingClientRect();
Explanation: If you put a non-existing element inside the document.getElementById(), then it throws an error to you, as in the given example 'nonExistentingElement' is placed, but no HTML element is available with this id.
Solution: Ensure the element is available in your HTML document before passing it in document.getElementById().
2. IntersectionObserver Not Supported
Issue: If your browser is not updated, then it will lead to an error like "IntersectionObserver is not a function."
Solution: Update your browser.
Conclusion
The above-discussed methods are the most efficient way to check if the DOM element is visible inside the viewport or not. By covering these methods, you have a good idea of everything that you need to know. By choosing the right method according to your needs, you can improve the performance and user experience of your website.
How to Check a DOM Element is Visible in Current Viewport - FAQs
1. How do I know if a DOM element exists?
You know simply by using document.getElementById(‘elementId’) and checking if it does not return any null value.
2. How do you check if an element is in the viewport scroll?
You can check it easily by using getBoundingClientRect() to compare its position with the boundaries of the viewport.
3. Can an element be in the DOM but not visible to the user?
Yes, it happens if the element is hidden using CSS properties like display: none or positioned outside the viewport
4. Is it necessary to check if every element is visible in the viewport?
No, it is not always necessary to check, but it’s useful for performance optimization, lazy loading, or triggering animations when you can see elements on the screen.
5. How can I check if a DOM element is partially visible in the viewport?
You can check it by using the getBoundingClientRect() method and comparing the element’s position with the viewport’s boundaries.