In modern web applications, it is common to have data that needs to be updated and synchronized with a server. One technique that can improve the user experience is optimistic updates, where the UI is updated immediately while the actual server call is in progress. This helps to make the application feel more responsive.

In this blog post, we will explore how we can implement optimistic updates using JavaScript Proxy. We will create a simple example to demonstrate the concept.

What is JavaScript Proxy?

Proxy is a built-in object in JavaScript that allows you to intercept and customize fundamental operations on objects. It enables us to define custom behavior for fundamental operations like getting and setting properties, function invocations, etc.

Implementing Optimistic Updates

Let’s say we have a todo list application, and we want to implement optimistic updates when marking a task as completed. Here’s how we can achieve it using JavaScript Proxy:

// Create a function to handle the actual update on the server
async function markTaskCompletedOnServer(taskId) {
  // Simulate server delay
  await delay(1000);
  // Make the API call to mark the task as completed
  // ...
}

// Create a proxy for the todo list object
const todoListProxy = new Proxy(todoList, {
  set(target, property, value) {
    // Intercept the set operation
    const oldValue = target[property];
    target[property] = value;

    // Check if the property being set is 'completed' and perform optimistic update
    if (property === 'completed') {
      markTaskCompletedOnServer(target.id);
    }

    // Return true to indicate success
    return true;
  },
});

// Usage
todoListProxy[0].completed = true;

In the code snippet above, we create a proxy object todoListProxy for the todoList object. We define a set trap on the proxy to intercept the assignment of the completed property. When the property is being set, we perform the optimistic update by calling the markTaskCompletedOnServer function, which simulates the asynchronous server call.

This way, the UI updates immediately with the completed state, giving the impression that the task is marked as completed instantly. Once the server call completes, the actual state on the server will be synced, and if there are any discrepancies, they can be handled accordingly.

Conclusion

Optimistic updates using JavaScript Proxy provide a powerful way to enhance the user experience in web applications. By intercepting and customizing object operations, we can update the UI optimistically while the server request is being processed. This gives the application a more responsive feel, improving the overall user experience.

#JavaScript #OptimisticUpdates