Dynamically Adding Classes in Svelte Using onMount

Description

Learn how to dynamically assign multiple classes to an input element in Svelte with the `onMount` lifecycle method. Effective solutions and troubleshooting tips included! --- This video is based on the question https://stackoverflow.com/q/63005913/ asked by the user 'Marco' ( https://stackoverflow.com/u/3254501/ ) and on the answer https://stackoverflow.com/a/63007971/ provided by the user 'digby280' ( https://stackoverflow.com/u/1390927/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: using onMount to add class dynamically to element Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Dynamically Adding Classes in Svelte Using onMount Creating dynamic components in Svelte can often present challenges, especially when working with styles. A common scenario arises when you're trying to add classes programmatically to an element, only to find that the intended styles are not applied. This post will guide you through the solution, specifically focusing on using the onMount lifecycle method to add classes dynamically to an input element. The Problem: Styles Not Applying In a typical Svelte application, you might be tempted to create an input element dynamically and apply specific classes—like "name" and "border"—to it. However, you encounter an issue where these classes do not properly apply, leading to unexpected styling results. Example Code Consider the following basic Svelte component: [[See Video to Reveal this Text or Code Snippet]] In this code, we've set up a simple component that adds an input element but struggles to apply the specified styles dynamically. The Solution: Global Styles The primary reason behind the styles not applying is that Svelte optimizes CSS by removing any unused styles during the build process. In the example above, since the styles are intended for elements created later through pure JavaScript, Svelte doesn't recognize them as being in use. Making Styles Global To ensure your styles are not discarded by Svelte, you should mark them as global using the :global modifier. This tells Svelte to preserve those styles regardless of whether the elements are present when the styles are defined within the component. Here is the corrected style section incorporating global styles: [[See Video to Reveal this Text or Code Snippet]] Code with Global Styles By applying the global styles, your full component code will look like this: [[See Video to Reveal this Text or Code Snippet]] Conclusion By making your styles global, you can successfully apply them to dynamically created elements in Svelte. Utilizing the onMount lifecycle method ensures that your JavaScript code runs after the component mounts, allowing you to manipulate the DOM safely. This approach opens the door for creating more dynamic and interactive user interfaces. Key Takeaway Always remember to check if your styles are being optimized away by Svelte. If they are not being used at compile-time, make them global!