Modern Full-Stack Development

 Bonus  Example
Let’s take this web server code just a little further to roll in some more NPM goodness, 
just to use almost everything discussed so far.
Chapter 1   Server-Side aCtion: node and npM

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19
To begin, let’s add a dependency to our project. We’re going to use the not-very- 
creatively-but-very-accurately-named request module, which will provide to our server 
an elementary HTTP client for it to use to make remote calls:
npm install request --save
With that done, copy that server.js file and name it server_time.js, then replace 
its contents with the following code:
require("http").createServer((inRequest, inResponse) => {
  const requestModule = require("request");
  requestModule(
    "http://worldtimeapi.org/api/timezone/America/New_York",
    function (inErr, inResp, inBody) {
      inResponse.end(
        `Hello from my first Node Web server: ${inBody}`
      );
    }
  );
}).listen(80);
As you probably recognize, it’s the same code as before, but now with a bit more 
inside the callback function provided to createServer(). What we’re doing now is 
firstly to import the request module and to give it the name requestModule (just to help 
disambiguate it from the inRequest object passed into the callback function). The API 
for this module is straightforward: pass a URL to the constructor, plus a callback, and 
a call will be made to the URL, and the provided callback will be executed when the 
response to that call comes back. The URL here is to the World Time API, which you 
can read about here: 
http://worldtimeapi.org
. This particular form of the URL (the 
API provides a few) takes in a time zone, America/New_York here (though you should 
certainly feel free to replace that with a time zone you prefer – you can access 
http://
worldtimeapi.org/api/timezone
 in a browser to see a list of available time zones). 
What we get back is a chunk of JSON, which is then written to the response that is 
returned to the browser.
Chapter 1   Server-Side aCtion: node and npM

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The final step is you’ll need to edit package.json to change that start value to 
indicate the new JavaScript file, after which you can launch the app and try it. The 
response you’ll see now isn’t necessarily pretty:
Hello from my first Node Web server: {"week_number":36,"utc_offset": 
"-04:00","utc_datetime":"2019-09-06T17:22:45.406437+00:00","unixtime": 
1567790565,"timezone":"America/New_York","raw_offset":-18000,"dst_until": 
"2019-11-03T06:00:00+00:00","dst_offset":3600,"dst_from":"2019- 03- 10T07: 
00:00+00:00","dst":true,"day_of_year":249,"day_of_week":5,"datetime": 
"2019-09-06T13:22:45.406437-04:00","client_ip":"12.198.42.69", 
"abbreviation":"EDT"}
…but it gets the job done (and, if like me, you have a browser extension that 
automatically “prettifies” JSON, then what you’ll see will be, well, prettier!).
This is a good example not only of adding dependencies to a project and using 
them but also of the asynchronous nature of Node I talked about earlier. Here, the 
call to the World Time API takes some time, and the response to the request coming 
from the browser is queued up and awaits that response before executing the callback 
passed to the requestModule() constructor, which then produces the final response to 
the browser. But, all that time, Node was free to handle other incoming requests; work 
wasn’t held up awaiting the remote request, that’s the key thing.