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Mastering JSObjectMakeDeferredPromise in JavascriptCore

Learn how to effectively use `JSObjectMakeDeferredPromise` in JavascriptCore with Flutter for asynchronous operations. Follow our detailed guide to fix common issues and understand the process better. --- This video is based on the question https://stackoverflow.com/q/65087037/ asked by the user 'noname.cs' ( https://stackoverflow.com/u/62844/ ) and on the answer https://stackoverflow.com/a/75733365/ provided by the user 'Truong Do' ( https://stackoverflow.com/u/150287/ ) 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: How to use JSObjectMakeDeferredPromise of JavascriptCore Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Mastering JSObjectMakeDeferredPromise in JavascriptCore: A Step-by-Step Guide As developers increasingly integrate JavaScript and Flutter, the need for smooth, asynchronous communication becomes paramount. One common challenge is effectively using the JSObjectMakeDeferredPromise function in JavascriptCore to ensure that asynchronous calls from JavaScript to Flutter work seamlessly. This guide aims to guide you through utilizing JSObjectMakeDeferredPromise effectively and troubleshooting common pitfalls you may encounter. Understanding the Problem In the case presented, the developer attempts to make an asynchronous call from JavaScript to Flutter using Flutter's flutter_jscore library. The intention is to call a function named getUser, which would respond back with user information after a brief delay. However, after calling the resolve function on the Flutter side, they found that the expected response never reaches the JavaScript execution context. Example Code Review Here's a breakdown of the provided code: JavaScript Context Initialization: The developer initializes a JS context and registers the getUser function. Flutter Function Logic: The Flutter function getUser creates and resolves a deferred promise after a simulated delay using fetchUser(). Despite being logically sound, the developer faced issues like: The JavaScript side not executing the then method after calling getUser. An unclear outcome from the promise resolution. The Solution To ensure that your promise behaves as expected, modifications need to be made to override the then function of the promise object. Below are detailed steps to implement this fix. Step 1: Override the then Function of the Promise The very first adjustment you need to make is to set up the then function for the promise you create. Here’s an example of how to implement this in your existing code structure: [[See Video to Reveal this Text or Code Snippet]] Step 2: Handle the Asynchronous Response After defining your promise and its then function, ensure that you correctly resolve or reject your promise based on the response from the Flutter side. Here's how you can manipulate the response received from a simulated HTTP call to ensure your promise is resolved properly: [[See Video to Reveal this Text or Code Snippet]] Step 3: Testing Your Code Once you implement the above changes, test your code with the following JavaScript calls: [[See Video to Reveal this Text or Code Snippet]] Conclusion Integrating Flutter with JavaScript can be complex, especially when dealing with promises and asynchronous calls. By following the steps outlined to properly override the then function and ensure that your promise is resolved correctly, you can fix the issues and achieve the desired behaviour in your code. This approach allows for smoother interactions between JavaScript and Flutter, leading to a more harmonious user experience. As you continue to explore the capabilities of JSObjectMakeDeferredPromise in JavascriptCore, remember that practice and experimentation go hand in hand. If you encounter any hurdles, refer to this guide to revisit the concepts and solutions presented. Happy Coding!