Stay Alert ⚠ with JavaScript: Using the Page Visibility API🚀
Tags: webdev, javascript, api, beginners
Published: 2024-05-30 11:30:54

### What's the Page Visibility API?
The Page Visibility API is a web API that allows developers to determine the visibility state of a webpage. This can be particularly useful for optimizing performance and improving user experience by controlling activities based on whether the page is in the foreground or background.

1. **Visibility States**:
   - **visible**: The page content is at least partially visible.
   - **hidden**: The page content is not visible to the user (e.g., minimized or another tab is active).

2. **Basic Usage**:
   - Access the API through `document.visibilityState` and listen for `visibilitychange` events.
   - Example:
     ```javascript
     if (document.visibilityState === 'hidden') {
       console.log('Page is hidden');
     } else {
       console.log('Page is visible');
     }
     ```

### How to Check Page Visibility Changes
Monitoring page visibility changes allows you to execute specific code when the visibility state changes.

1. **Event Listener Setup**:
   - Add an event listener for the `visibilitychange` event.
     ```javascript
     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         console.log('User switched to another tab');
       } else {
         console.log('User returned to the tab');
       }
     });
     ```

2. **Handling Visibility Changes**:
   - Example: Pause a video when the page is hidden and resume when visible.
     ```javascript
     const video = document.querySelector('video');

     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         video.pause();
       } else {
         video.play();
       }
     });
     ```

### Why Page Visibility is Useful
Utilizing the Page Visibility API can significantly enhance the performance and user experience of your web applications.

1. **Performance Optimization**:
   - Pause or throttle resource-intensive tasks when the page is not visible.
     ```javascript
     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         stopHeavyComputations();
       } else {
         startHeavyComputations();
       }
     });
     ```

2. **User Experience Improvements**:
   - Example: Pause animations or videos to save battery and CPU usage.
     ```javascript
     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         pauseAnimations();
       } else {
         resumeAnimations();
       }
     });
     ```

3. **Background Tasks**:
   - Manage background data syncing or notifications more efficiently.
     ```javascript
     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         startDataSync();
       } else {
         stopDataSync();
       }
     });
     ```

### Patterns to Avoid with Page Visibility Checks
While the Page Visibility API is powerful, there are certain practices to avoid to ensure optimal performance and user experience.

1. **Avoid Excessive Polling**:
   - Do not use the API to constantly poll for visibility state. Use event listeners instead.
     ```javascript
     // Bad practice:
     setInterval(() => {
       if (document.visibilityState === 'hidden') {
         console.log('Page is hidden');
       }
     }, 1000);
     ```

2. **Avoid Ignoring User Intent**:
   - Ensure that actions taken based on visibility changes align with user expectations.
     ```javascript
     // Avoid forcing actions that might disrupt user experience
     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         muteAudio();
       } else {
         unmuteAudio();
       }
     });
     ```

3. **Avoid Heavy Operations on Visibility Change**:
   - Do not perform heavy operations in response to visibility changes as it can lead to poor performance.
     ```javascript
     document.addEventListener('visibilitychange', () => {
       if (document.visibilityState === 'hidden') {
         // Avoid heavy computations here
       }
     });
     ```

### Summary
The Page Visibility API is a versatile tool for managing page activity based on visibility state. By understanding how to check for visibility changes and leveraging this API, you can optimize performance and enhance user experience. Remember to use the API responsibly, avoiding patterns that could negatively impact performance or user expectations.