Using promises for server-side rendering in Javascript

26 Oct 2023

server

In modern web development, server-side rendering (SSR) has gained popularity due to its ability to improve performance and user experience. JavaScript frameworks like React and Vue have built-in support for SSR, allowing developers to render their UI components on the server before sending the page to the client.

When implementing SSR, dealing with asynchronous operations can be a bit tricky. JavaScript Promises provide a clean and elegant solution for managing async operations on the server. In this blog post, we will explore how to use promises for server-side rendering in JavaScript.

Understanding Promises

Promises are objects that represent the eventual completion (or failure) of an asynchronous operation. They have three states:

Pending: The initial state, indicating that the operation is still in progress.
Fulfilled: The state when the operation has been completed successfully.
Rejected: The state when an error occurred during the operation.

Promises expose methods like then() and catch() to handle the fulfillment or rejection of the operation. These methods take callback functions as arguments, allowing you to run code based on the promise’s state.

Server-Side Rendering with Promises

To use promises for server-side rendering, you’ll typically follow these steps:

Fetch the required data asynchronously.
Create a promise that resolves when all the necessary data has been fetched.
Render your UI components using the resolved data.
Send the rendered page to the client.

Let’s see an example of how this can be done using JavaScript and a popular SSR framework, Next.js:

// Import required modules
import fetch from 'node-fetch';
import { Promise } from 'bluebird';
import { renderToString } from 'react-dom/server';
import App from './App';

// Create a promise that fetches the required data
const fetchData = () => {
  return new Promise((resolve, reject) => {
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => resolve(data))
      .catch(error => reject(error));
  });
};

// Use fetchData to fetch the data asynchronously
fetchData()
  .then(data => {
    // Render the React component to a string
    const html = renderToString(<App data={data} />);

    // Send the rendered page to the client
    res.send(`
      <!DOCTYPE html>
      <html>
        <head>
          <title>Server-Side Rendering with Promises</title>
        </head>
        <body>
          <div id="root">${html}</div>
          <script src="client.js"></script>
        </body>
      </html>
    `);
  })
  .catch(error => {
    // Handle error
    console.error('Error:', error);
    res.status(500).send('Internal Server Error');
  });

In the example above, we create a promise fetchData() that fetches data from an API endpoint. We then use the resolved data to render our React component (<App />) using renderToString(). Finally, we send the rendered page to the client.

By using promises, we can ensure that the data is fetched and the rendering is completed before sending the page to the client. This prevents partial rendering or sending incomplete UI components to the user.

Conclusion

Promises are a powerful tool for managing async operations in JavaScript, making them ideal for server-side rendering. By utilizing promises, you can ensure that your server-side rendering process is reliable and efficient. Whether you’re using frameworks like Next.js or implementing your custom SSR solution, promises provide a clean and structured approach to handle async tasks during server-side rendering.

With proper implementation, promises can greatly enhance the performance and user experience of your server-rendered applications.

Understanding Promises

Server-Side Rendering with Promises

Conclusion

References