How to Effectively Pass onMount JSON Data to a Variable in Svelte

Description

Learn how to store JSON data fetched using Svelte's onMount in a variable that can be accessed globally within your component. --- This video is based on the question https://stackoverflow.com/q/64567137/ asked by the user 'Denise' ( https://stackoverflow.com/u/8720051/ ) and on the answer https://stackoverflow.com/a/64567348/ provided by the user 'Stephane Vanraes' ( https://stackoverflow.com/u/11956107/ ) 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: Pass onmount json to variable 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. --- How to Effectively Pass onMount JSON Data to a Variable in Svelte Using Svelte to fetch data can sometimes lead to challenges, especially when trying to access that data outside the onMount lifecycle function. If you've ever found yourself in a situation where you need to use data fetched with onMount in other parts of your component, you're not alone! In this guide, we'll break down how to properly handle JSON data retrieved with onMount, ensuring that you can store it in a variable for later use. The Problem: Fetching JSON Data with onMount In Svelte, the onMount lifecycle function is commonly used to execute code after the component has been created. However, one challenge arises when trying to access data fetched inside onMount outside of that function. Here’s a look at a simple example where an issue occurs: [[See Video to Reveal this Text or Code Snippet]] As shown, the console.log(testData) statement placed outside onMount returns an empty array because it executes before the asynchronous call to fetch the data completes. The Solution: Using Reactive Statements To properly access your fetched testData at any point in your component, you can utilize Svelte's reactive declarations. Here's how you can revise your code: Step 1: Incorporate a Reactive Statement You can use Svelte’s reactive statement syntax, which is denoted by the $: prefix. This allows you to run a block of code whenever the specified variables change. Here’s how to implement it: [[See Video to Reveal this Text or Code Snippet]] Step 2: Understanding What Happens By adding the reactive statement, every time testData is updated (once the JSON is fetched), this line will automatically execute. It gives you two logs in the console: The initial value of testData, which is still an empty array [] at the start. The updated value of testData after the fetch completes, which will show your actual data. Complete Example Here is your modified code with the reactive statement included: [[See Video to Reveal this Text or Code Snippet]] Conclusion By leveraging Svelte's reactive statements, you can easily manage and access your fetched data outside of the onMount function. This adjustment not only enhances your code’s readability but also makes it much easier to debug data flow within your components. Keep experimenting with Svelte's reactivity to optimize your data handling further! Happy coding!