Understanding Chrome’s Scheduler.yield API

Hey there! 👋 I’m Lakin, and today we’re going to learn about a new and exciting tool for web developers: Chrome’s Scheduler.yield API. Don’t worry if you’re new to this — I will explain everything step by step with easy examples.

What is Scheduler.yield API?

Scheduler.yield API is a new feature in Chrome’s JavaScript. It helps make websites faster and smoother. Think of it like a traffic signal for your code. It tells your JavaScript when to pause and let other important tasks happen.

Why is it important?

Sometimes, when a website is doing a lot of work, it can become slow or unresponsive. This happens because JavaScript is busy and can’t handle other tasks like responding to clicks or showing animations. Scheduler.yield API helps solve this problem.

How does Scheduler.yield work?

Let’s break it down with a simple example:

Imagine you’re cooking a big meal. You have to chop vegetables, boil rice, and fry chicken. If you do all these tasks without a break, you might get tired and make mistakes. But if you take small breaks between tasks, you’ll cook better and have energy to set the table too.

Scheduler.yield works the same way for your JavaScript code. It allows your code to take small breaks, letting the browser do other important things.

Here’s a simple code example:

async function doManyCalculations() {
  for (let i = 0; i < 1000000; i++) {
    // Do some calculation
    let result = i * 2;
    
    // Every 10000 calculations, take a break
    if (i % 10000 === 0) {
      await scheduler.yield();
    }
  }
}

In this example, the function does a million calculations. But every 10,000 calculations, it uses scheduler.yield() to take a short break. This allows the browser to handle other tasks if needed.

Why should we use Scheduler.yield?

Using Scheduler.yield has many benefits:

1. Better user experience: Your website stays responsive even when doing complex tasks.
2. Smoother animations: Animations and scrolling work better because the browser has time to update the screen.
3. Faster overall: The website feels faster because it’s not getting stuck on one big task.

Real-life examples of using Scheduler.yield

Let’s look at some situations where Scheduler.yield can help:

Example 1: Processing a large list of items

Imagine you have a website that shows a list of 10,000 products. Loading all at once might make the page slow. Here’s how you can use Scheduler.yield:

async function loadProducts(products) {
  for (let i = 0; i < products.length; i++) {
    // Add product to page
    addProductToPage(products[i]);
    
    // Every 50 products, take a break
    if (i % 50 === 0) {
      await scheduler.yield();
    }
  }
}

This code loads products in small groups, taking breaks to keep the page responsive.

Example 2: Complex calculation

If your website needs to do a complex calculation, like finding prime numbers, you can use Scheduler.yield to keep the page responsive:

async function findPrimes(max) {
  for (let i = 2; i <= max; i++) {
    if (isPrime(i)) {
      console.log(i + " is prime");
    }
    
    // Take a break every 1000 numbers
    if (i % 1000 === 0) {
      await scheduler.yield();
    }
  }
}

function isPrime(num) {
  for (let i = 2; i <= Math.sqrt(num); i++) {
    if (num % i === 0) return false;
  }
  return num > 1;
}

This function finds prime numbers but takes breaks regularly, allowing other parts of the website to work smoothly.

Example 3: Handling Large Data Processing Efficiently

Imagine you’re developing a web application that processes thousands of images, applies filters to each, and displays the progress in a progress bar. Without optimization, such tasks can freeze the browser, making the UI unresponsive.

We can avoid this by using scheduler.yield(), which pauses the task periodically, giving the browser a chance to update the UI and handle other events.

Here’s an example of how to process a large dataset (in this case, applying filters to images) while maintaining a smooth user experience:

async function processImages(images) {
  const processedImages = [];
  
  for (let i = 0; i < images.length; i++) {
    processedImages.push(applyImageFilter(images[i])); // Simulate heavy processing
    
    // Pause every 50 images to allow UI updates
    if (i % 50 === 0) {
      await scheduler.yield(); 
      updateProgressBar((i / images.length) * 100); // Update progress bar
    }
  }
  return processedImages;
}

function applyImageFilter(image) {
  // Simulate complex image processing
  let processedImage = image;
  for (let i = 0; i < 500000; i++) {
    processedImage += Math.tan(i) * Math.sqrt(i);  // Fake complex computation
  }
  return processedImage;
}
function updateProgressBar(percentage) {
  // Update progress bar in the UI
  document.getElementById('progress-bar').style.width = percentage + '%';
}

Applications and Benefits:

Using scheduler.yield() is particularly useful for applications with intensive computations or those that need to maintain a smooth user interface:

• Image Processing Tools: Applications that allow users to apply filters or effects to multiple images.
• Data Visualizations: Processing large amounts of data in real-time without causing the browser to freeze.
• Games: Browser games that require frequent computations while ensuring that the user interface remains responsive.
• Text Editors: Processing large documents while keeping the text editor responsive.

How to start using Scheduler.yield

If you’re a developer, you can start using scheduler.yield in your code right now! But there's a catch - it's still pretty new, so not all web browsers support it yet. Here's what you need to know:

1. It works in newer versions of Chrome.
2. For other browsers, you might need to use a backup plan (I’ll show you one in a bit).
3. You can check if it’s available like this:

if ("scheduler" in window && "yield" in scheduler) {
  console.log("We can use scheduler.yield!");
} else {
  console.log("Oops, scheduler.yield isn't available.");
}

What If It Doesn’t Work?

No worries! If scheduler.yield isn't available, you can use a simple trick that works almost as well:

async function takeAQuickBreak() {
  if ("scheduler" in window && "yield" in scheduler) {
    await scheduler.yield();
  } else {
    await new Promise(resolve => setTimeout(resolve, 0));
  }
}

This tells the browser to wait just a tiny bit, which can often be enough to keep things running smoothly.

Important Points:

1. Use Chrome version 129 or newer.

2. If you’re using an older version, go to chrome://flags in your browser, search for "scheduler.yield", and turn it on.

3. In your JavaScript code, use await scheduler.yield() in places where you want to give the browser a chance to do other tasks.

Wrapping Up

Scheduler.yield API is a powerful tool that can make your websites faster and smoother. By adding small breaks in your code, you allow the browser to manage tasks better, resulting in a better experience for your users.

Remember:

• Use it in long tasks or loops
• Don’t use it too often, or your task might take too long to finish
• Test your website to find the right balance

I hope this guide helps you understand and use Scheduler.yield API. If you have any questions, feel free to ask in the comments below.

Happy coding, everyone! 😊

References :

Introducing the scheduler.yield origin trial | Blog | Chrome for Developers