postJSON.js

const https = require("https");

/*
 * Convert the body object to a JSON string then HTTPS POST it to the
 * specified API endpoint on the specified host. When the response arrives,
 * parse the response body as JSON and resolve the returned Promise with
 * that parsed value.
 */
function postJSON(host, endpoint, body, port, username, password) {
    // Return a Promise object immediately, then call resolve or reject
    // when the HTTPS request succeeds or fails.
    return new Promise((resolve, reject) => {
        // Convert the body object to a string
        let bodyText = JSON.stringify(body);

        // Configure the HTTPS request
        let requestOptions = {
            method: "POST",       // Or "GET", "PUT", "DELETE", etc.
            host: host,           // The host to connect to
            path: endpoint,       // The URL path
            headers: {            // HTTP headers for the request
                "Content-Type": "application/json",
                "Content-Length": Buffer.byteLength(bodyText)
            }
        };

        if (port) {                      // If a port is specified,
            requestOptions.port = port;  // use it for the request.
        }
        // If credentials are specified, add an Authorization header.
        if (username && password) {
            requestOptions.auth = `${username}:${password}`;
        }

        // Now create the request based on the configuration object
        let request = https.request(requestOptions);

        // Write the body of the POST request and end the request.
        request.write(bodyText);
        request.end();

        // Fail on request errors (such as no network connection)
        request.on("error", e => reject(e));

        // Handle the response when it starts to arrive.
        request.on("response", response => {
            if (response.statusCode !== 200) {
                reject(new Error(`HTTP status ${response.statusCode}`));
                // We don't care about the response body in this case, but
                // we don't want it to stick around in a buffer somewhere, so
                // we put the stream into flowing mode without registering
                // a "data" handler so that the body is discarded.
                response.resume();
                return;
            }

            // We want text, not bytes. We're assuming the text will be
            // JSON-formatted but aren't bothering to check the
            // Content-Type header.
            response.setEncoding("utf8");

            // Node doesn't have a streaming JSON parser, so we read the
            // entire response body into a string.
            let body = "";
            response.on("data", chunk => { body += chunk; });

            // And now handle the response when it is complete.
            response.on("end", () => {          // When the response is done,
                try {                           // try to parse it as JSON
                    resolve(JSON.parse(body));  // and resolve the result.
                } catch(e) {                    // Or, if anything goes wrong,
                    reject(e);                  // reject with the error
                }
            });
        });
    });
}