React useFormStatus Progress Estimation: Completion Time Prediction

React's useFormStatus hook, introduced in React 18, provides valuable information about the status of a form submission. While it doesn't directly offer progress estimation, we can leverage its properties and other techniques to provide users with meaningful feedback during potentially long-running form submissions. This post explores methods for estimating progress and predicting completion time when using useFormStatus, resulting in a more engaging and user-friendly experience.

Understanding useFormStatus

Before diving into progress estimation, let's quickly recap the purpose of useFormStatus. This hook is designed to be used within a <form> element that utilizes the action prop. It returns an object containing the following properties:

• pending: A boolean indicating whether the form is currently submitting.
• data: The data that was submitted with the form (if the submission was successful).
• method: The HTTP method used for the form submission (e.g., 'POST', 'GET').
• action: The function passed to the form's action prop.
• error: An error object if the submission failed.

While useFormStatus tells us if the form is submitting, it doesn't give any direct information about the progress of the submission, especially if the action function involves complex or lengthy operations.

The Challenge of Progress Estimation

The core challenge lies in the fact that the action function's execution is opaque to React. We don't inherently know how far along the process is. This is especially true for server-side operations. However, we can employ various strategies to overcome this limitation.

Strategies for Progress Estimation

Here are several approaches you can take, each with its own trade-offs:

1. Server-Sent Events (SSE) or WebSockets

The most robust solution is often to push progress updates from the server to the client. This can be achieved using:

• Server-Sent Events (SSE): A unidirectional (server-to-client) protocol that allows the server to push updates to the client over a single HTTP connection. SSE is ideal when the client only needs to *receive* updates.
• WebSockets: A bidirectional communication protocol that provides a persistent connection between the client and server. WebSockets are suitable for real-time updates in both directions.

Example (SSE):

Server-side (Node.js):

            const express = require('express');
const app = express();

app.get('/progress', (req, res) => {
  res.setHeader('Content-Type', 'text/event-stream');
  res.setHeader('Cache-Control', 'no-cache');
  res.setHeader('Connection', 'keep-alive');
  res.flushHeaders();

  let progress = 0;
  const interval = setInterval(() => {
    progress += 10;
    if (progress > 100) {
      progress = 100;
      clearInterval(interval);
      res.write(`data: {"progress": ${progress}, "completed": true}\n\n`);
      res.end();
    } else {
      res.write(`data: {"progress": ${progress}, "completed": false}\n\n`);
    }
  }, 500); // Simulate progress update every 500ms
});

app.listen(3000, () => {
  console.log('Server listening on port 3000');
});

            

              
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Client-side (React):

            import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [progress, setProgress] = useState(0);

  useEffect(() => {
    const eventSource = new EventSource('/progress');

    eventSource.onmessage = (event) => {
      const data = JSON.parse(event.data);
      setProgress(data.progress);

      if (data.completed) {
        eventSource.close();
      }
    };

    eventSource.onerror = (error) => {
      console.error('EventSource failed:', error);
      eventSource.close();
    };

    return () => {
      eventSource.close();
    };
  }, []);

  return (
    <div>
      <p>Progress: {progress}%</p>
    </div>
  );
}

export default MyComponent;

            

              
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Explanation:

• The server sets the appropriate headers for SSE.
• The server sends progress updates as data: events. Each event is a JSON object containing the progress and a completed flag.
• The React component uses EventSource to listen for these events.
• The component updates the state (progress) based on the received events.

Advantages: Accurate progress updates, real-time feedback.

Disadvantages: Requires server-side changes, more complex implementation.

2. Polling with an API Endpoint

If you can't use SSE or WebSockets, you can implement polling. The client periodically sends requests to the server to check the status of the operation.

Example:

Server-side (Node.js):

            const express = require('express');
const app = express();

// Simulate a long-running task
let taskProgress = 0;
let taskId = null;

app.post('/start-task', (req, res) => {
  taskProgress = 0;
  taskId = Math.random().toString(36).substring(2, 15) + Math.random().toString(36).substring(2, 15); // Generate a unique task ID

  // Simulate background processing
  const interval = setInterval(() => {
    taskProgress += 10;
    if (taskProgress >= 100) {
      taskProgress = 100;
      clearInterval(interval);
    }
  }, 500);

  res.json({ taskId });
});

app.get('/task-status/:taskId', (req, res) => {
  if (req.params.taskId === taskId) {
    res.json({ progress: taskProgress });
  } else {
    res.status(404).json({ message: 'Task not found' });
  }
});

app.listen(3000, () => {
  console.log('Server listening on port 3000');
});

            

              
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Client-side (React):

            import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [progress, setProgress] = useState(0);
  const [taskId, setTaskId] = useState(null);

  const startTask = async () => {
    const response = await fetch('/start-task', { method: 'POST' });
    const data = await response.json();
    setTaskId(data.taskId);
  };

  useEffect(() => {
    if (!taskId) return;

    const interval = setInterval(async () => {
      const response = await fetch(`/task-status/${taskId}`);
      const data = await response.json();
      setProgress(data.progress);

      if (data.progress === 100) {
        clearInterval(interval);
      }
    }, 1000); // Poll every 1 second

    return () => clearInterval(interval);
  }, [taskId]);

  return (
    <div>
      <button onClick={startTask} disabled={taskId !== null}>Start Task</button>
      {taskId && <p>Progress: {progress}%</p>}
    </div>
  );
}

export default MyComponent;

            

              
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Explanation:

• The client starts a task by calling /start-task, receiving a taskId.
• The client then polls /task-status/:taskId periodically to get the progress.

Advantages: Relatively simple to implement, doesn't require persistent connections.

Disadvantages: Can be less accurate than SSE/WebSockets, introduces latency due to polling interval, puts load on server due to frequent requests.

3. Optimistic Updates and Heuristics

In some cases, you can use optimistic updates combined with heuristics to provide a reasonable estimate. For example, if you're uploading files, you can track the number of bytes uploaded client-side and estimate progress based on the total file size.

Example (File Upload):

            import React, { useState } from 'react';

function MyComponent() {
  const [progress, setProgress] = useState(0);
  const [file, setFile] = useState(null);

  const handleFileChange = (event) => {
    setFile(event.target.files[0]);
  };

  const handleSubmit = async (event) => {
    event.preventDefault();
    if (!file) return;

    const formData = new FormData();
    formData.append('file', file);

    try {
      const xhr = new XMLHttpRequest();
      xhr.upload.addEventListener('progress', (event) => {
        if (event.lengthComputable) {
          const percentage = Math.round((event.loaded * 100) / event.total);
          setProgress(percentage);
        }
      });

      xhr.open('POST', '/upload'); // Replace with your upload endpoint
      xhr.send(formData);

      xhr.onload = () => {
        if (xhr.status === 200) {
          console.log('Upload complete!');
        } else {
          console.error('Upload failed:', xhr.status);
        }
      };

      xhr.onerror = () => {
        console.error('Upload failed');
      };

    } catch (error) {
      console.error('Upload error:', error);
    }
  };

  return (
    <div>
      <form onSubmit={handleSubmit}>
        <input type="file" onChange={handleFileChange} />
        <button type="submit" disabled={!file}>Upload</button>
      </form>
      <p>Progress: {progress}%</p>
    </div>
  );
}

export default MyComponent;

            

              
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Explanation:

• The component uses an XMLHttpRequest object to upload the file.
• The progress event listener on xhr.upload is used to track the upload progress.
• The loaded and total properties of the event are used to calculate the percentage complete.

Advantages: Client-side only, can provide immediate feedback.

Disadvantages: Accuracy depends on the reliability of the heuristic, may not be suitable for all types of operations.

4. Breaking Down the Action into Smaller Steps

If the action function performs multiple distinct steps, you can update the UI after each step to indicate progress. This requires modifying the action function to provide updates.

Example:

            import React, { useState } from 'react';

async function myAction(setProgress) {
  setProgress(10);
  await someAsyncOperation1();
  setProgress(40);
  await someAsyncOperation2();
  setProgress(70);
  await someAsyncOperation3();
  setProgress(100);
}

function MyComponent() {
  const [progress, setProgress] = useState(0);

  const handleSubmit = async () => {
    await myAction(setProgress);
  };

  return (
    <div>
      <form onSubmit={handleSubmit}>
        <button type="submit">Submit</button>
      </form>
      <p>Progress: {progress}%</p>
    </div>
  );
}

export default MyComponent;

            

              
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Explanation:

• The myAction function accepts a setProgress callback.
• It updates the progress state at various points during its execution.

Advantages: Direct control over progress updates.

Disadvantages: Requires modifying the action function, can be more complex to implement if the steps are not easily divisible.

Predicting Completion Time

Once you have progress updates, you can use them to predict the estimated time remaining. A simple approach is to track the time taken to reach a certain progress level and extrapolate to estimate the total time.

Example (Simplified):

            import React, { useState, useEffect, useRef } from 'react';

function MyComponent() {
  const [progress, setProgress] = useState(0);
  const [estimatedTimeRemaining, setEstimatedTimeRemaining] = useState(null);
  const startTimeRef = useRef(null);

  useEffect(() => {
    if (progress > 0 && startTimeRef.current === null) {
      startTimeRef.current = Date.now();
    }

    if (progress > 0) {
      const elapsedTime = Date.now() - startTimeRef.current;
      const estimatedTotalTime = (elapsedTime / progress) * 100;
      const remainingTime = estimatedTotalTime - elapsedTime;
      setEstimatedTimeRemaining(Math.max(0, remainingTime)); // Ensure non-negative
    }
  }, [progress]);

  // ... (rest of the component and progress updates as described in previous sections)

  return (
    <div>
      <p>Progress: {progress}%</p>
      {estimatedTimeRemaining !== null && (
        <p>Estimated Time Remaining: {Math.round(estimatedTimeRemaining / 1000)} seconds</p>
      )}
    </div>
  );
}

export default MyComponent;

            

              
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Explanation:

• We store the start time when the progress is first updated.
• We calculate the elapsed time and use it to estimate the total time.
• We calculate the remaining time by subtracting the elapsed time from the estimated total time.

Important Considerations:

• Accuracy: This is a *very* simplified prediction. Network conditions, server load, and other factors can significantly impact the accuracy. More sophisticated techniques, like averaging over multiple intervals, can improve accuracy.
• Visual Feedback: Clearly indicate that the time is an *estimate*. Displaying ranges (e.g., "Estimated time remaining: 5-10 seconds") can be more realistic.
• Edge Cases: Handle edge cases where the progress is very slow initially. Avoid dividing by zero or displaying excessively large estimates.

Combining useFormStatus with Progress Estimation

While useFormStatus itself doesn't provide progress information, you can use its pending property to enable or disable the progress indicator. For example:

            import React, { useState } from 'react';
import { useFormStatus } from 'react-dom';

// ... (Progress estimation logic from previous examples)

function MyComponent() {
  const [progress, setProgress] = useState(0);
  const { pending } = useFormStatus();

  const handleSubmit = async (formData) => {
    // ... (Your form submission logic, including updates to progress)
  };

  return (
    <form action={handleSubmit}>
      <button type="submit" disabled={pending}>Submit</button>
      {pending && <p>Progress: {progress}%</p>}
    </form>
  );
}

            

              
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In this example, the progress indicator is only displayed while the form is pending (i.e., while useFormStatus.pending is true).

Best Practices and Considerations

• Prioritize Accuracy: Choose a progress estimation technique that is appropriate for the type of operation being performed. SSE/WebSockets generally provide the most accurate results, while heuristics may be sufficient for simpler tasks.
• Provide Clear Visual Feedback: Use progress bars, spinners, or other visual cues to indicate that an operation is in progress. Clearly label the progress indicator and, if applicable, the estimated time remaining.
• Handle Errors Gracefully: If an error occurs during the operation, display an informative error message to the user. Avoid leaving the progress indicator stuck at a certain percentage.
• Optimize Performance: Avoid performing computationally expensive operations in the UI thread, as this can negatively impact performance. Use web workers or other techniques to offload work to background threads.
• Accessibility: Ensure that progress indicators are accessible to users with disabilities. Use ARIA attributes to provide semantic information about the progress of the operation. For example, use aria-valuenow, aria-valuemin, and aria-valuemax on a progress bar.
• Localization: When displaying estimated time remaining, be mindful of different time formats and regional preferences. Use a library like date-fns or moment.js to format the time appropriately for the user's locale.
• Internationalization: Error messages and other text should be internationalized to support multiple languages. Use a library like i18next to manage translations.

Conclusion

While React's useFormStatus hook doesn't directly provide progress estimation capabilities, you can combine it with other techniques to provide users with meaningful feedback during form submissions. By using SSE/WebSockets, polling, optimistic updates, or breaking down actions into smaller steps, you can create a more engaging and user-friendly experience. Remember to prioritize accuracy, provide clear visual feedback, handle errors gracefully, and optimize performance to ensure a positive experience for all users, regardless of their location or background.

Further Exploration

• React useFormStatus Documentation
• Server-Sent Events (SSE)
• WebSockets
• XMLHttpRequest