getText.js

const https = require("https");

// Read the text content of the URL and asynchronously pass it to the callback.
function getText(url, callback) {
    // Start an HTTP GET request for the URL
    request = https.get(url);

    // Register a function to handle the "response" event.
    request.on("response", response => {
        // The response event means that response headers have been received
        let httpStatus = response.statusCode;

        // The body of the HTTP response has not been received yet.
        // So we register more event handlers to to be called when it arrives.
        response.setEncoding("utf-8");  // We're expecting Unicode text
        let body = "";                  // which we will accumulate here.

        // This event handler is called when a chunk of the body is ready
        response.on("data", chunk => { body += chunk; });

        // This event handler is called when the response is complete
        response.on("end", () => {
            if (httpStatus === 200) {   // If the HTTP response was good
                callback(null, body);   // Pass response body to the callback
            } else {                    // Otherwise pass an error
                callback(httpStatus, null);
            }
        });
    });

    // We also register an event handler for lower-level network errors
    request.on("error", (err) => {
        callback(err, null);
    });
}