How do you use Cheerio with asynchronous JavaScript code?

Cheerio is a fast, flexible, and lean implementation of core jQuery designed specifically for the server to parse, manipulate, and render HTML. When using Cheerio with asynchronous JavaScript code, especially in the context of web scraping or handling HTML content fetched from external sources, you'll often be working with promises or async/await syntax to handle asynchronous operations.

Below is an example of how you might use Cheerio with asynchronous JavaScript, such as when fetching HTML content using the axios HTTP client (or any other promise-based HTTP client library).

Using Cheerio with Async/Await

First, you'll need to install cheerio and axios:

npm install cheerio axios

Then, you can use the following code to fetch a web page and process it with Cheerio:

const axios = require('axios');
const cheerio = require('cheerio');

// Asynchronous function to fetch and process HTML content
async function fetchAndProcess(url) {
    try {
        // Fetch the HTML content from the URL
        const response = await axios.get(url);
        const html = response.data;

        // Load the HTML content into Cheerio
        const $ = cheerio.load(html);

        // Now you can use Cheerio to query and manipulate the HTML, similar to jQuery
        // For example, let's extract all the links from the page
        const links = [];
        $('a').each((index, element) => {
            links.push({
                text: $(element).text(),
                href: $(element).attr('href')
            });
        });

        // Return the extracted links
        return links;
    } catch (error) {
        console.error('Error fetching or processing:', error);
        throw error; // or handle error as needed
    }
}

// Using the function to get links from a web page
const url = 'https://example.com';
fetchAndProcess(url)
    .then(links => {
        console.log('Extracted links:', links);
    })
    .catch(error => {
        console.error('An error occurred:', error);
    });

In this example, fetchAndProcess is an asynchronous function that uses axios.get to fetch HTML content from the given URL. The HTML is then loaded into Cheerio using cheerio.load, allowing you to manipulate and query the HTML with a familiar jQuery-like API.

The $('a').each(...) loop is used to iterate over all anchor tags and extract their text and href attributes, storing the result in the links array.

Error Handling

Note that in the fetchAndProcess function, we're using a try-catch block to handle any errors that might occur during the fetching or processing of the HTML content. This is important because both the network request and the HTML parsing could potentially fail, and you'll want to handle these errors appropriately.

Conclusion

When you use Cheerio with asynchronous JavaScript code, you'll typically be wrapping it in an asynchronous function and using await to handle the promises returned by network requests or other asynchronous operations. Remember to handle errors appropriately, and you'll find that Cheerio integrates seamlessly into modern asynchronous JavaScript workflows.