REPL

With this video tutorial, lets learn about testing our code snippets using REPL, before implementing it into the actual node application. And then, we’ll show you how to add routes to your node server.

In this tutorial, we create 5 routes to the server:
“/” to “Home Page”
“/about” to “About Us”
“/contact” to “Contact Us”
/”satish” redirected to “Home Page”
anything else to “Page Not Found”

Command Prompt
Console Window

C:\>node
> var url = require("url");
undefined
> var myURL = "http://Technotip.org:3030/about";
undefined
> url
{ parse: [Function: urlParse],
  resolve: [Function: urlResolve],
  resolveObject: [Function: urlResolveObject],
  format: [Function: urlFormat],
  Url: [Function: Url] }
> url.parse(myURL).hostname;
'technotip.org'
> url.parse(myURL).port;
'3030'
> url.parse(myURL).pathname;
'/about'
>

Here we test our code snippets on the command prompt, before implementing it into our actual application. Working with node url module on command prompt, we learnt to make use of parse() method of url object to fetch the hostname, port and the pathname of the actual URL. We are interested in pathname – we’ll be using it in our node application.

Related Read: Read Evaluate Print Loop (RELP): Node.js

JavaScript File
app.js

var url= require("url");
var http= require("http");
 
     http.createServer(function(req, res){
 
var pathname= url.parse(req.url).pathname;
 
if( pathname === '/' )
{
res.writeHead(200, { "Content-Type": "text/plain" });
res.end("Home Page");
}
else if( pathname === '/about' )
{
res.writeHead(200, { "Content-Type": "text/plain" });
res.end("About Us");
}
else if( pathname === '/contact')
{
res.writeHead(200, { "Content-Type": "text/plain" });
res.end("Contact Us");
}
else if( pathname === '/satish' )
{
res.writeHead(301, { "Location": "/" });
res.end("Home Page");
}
else
{
res.writeHead(404, { "Content-Type": "text/plain" });
res.end("Page Not Found!!");
}
   }).listen("8080", "127.0.0.1");
 console.log("Server running ..");

Here we require url and http module. Using http object we create HTTP Server. Using url object we call parse method to parse and fetch the path from the user request URL.

Once we fetch the path, using conditional statements we display the corresponding message with appropriate response header information. We also illustrate 301 redirection

Adding Routes to Your Server: Node.js

[youtube https://www.youtube.com/watch?v=ejER-HVhDm8]

YouTube Link: https://www.youtube.com/watch?v=ejER-HVhDm8 [Watch the Video In Full Screen.]

Note: Make sure to turn on the server before trying to access the server!
execution code
command prompt

 
C:\>cd node
 
C:\node>node app.js
Server running ..

Navigate to the folder where you’ve your app.js file located, and run the server by executing the script using node command.

Today let us see REPL in Node.js

Most programming languages provide REPL facility to test and debug the code, and Node.js is no different in this approach.

Command Prompt
Console Window

C:\>node
> 1 + 1
2
> var a;
undefined
> a = 10
10
> a + 5
15
> a
10
> ++a
11
> a++
11
> a
12
> "Satish "+"B"
'Satish B'
> function technotip() { return 101; }
undefined
> technotip();
101
>2

Here we can type in our valid code snippet and instantly get the results. Some of the things we can do are: arithmetic operations, string manipulations, pre and post increment decrement of numbers, method declaration and defining and calling the methods etc.

We could even require some built-in node modules and using its objects we can look at the methods and properties it provides.
Command Prompt
Console Window

> var http = require("http");
undefined
> http.STATUS_CODES
{ '100': 'Continue',
  '101': 'Switching Protocols',
  '102': 'Processing',
  '200': 'OK',
  '201': 'Created',
  '202': 'Accepted',
  '203': 'Non-Authoritative Information',
  '204': 'No Content',
  '205': 'Reset Content',
  '206': 'Partial Content',
  '207': 'Multi-Status',
  '300': 'Multiple Choices',
  '301': 'Moved Permanently',
  '302': 'Moved Temporarily',
  '303': 'See Other',
  '304': 'Not Modified',
  '305': 'Use Proxy',
  '307': 'Temporary Redirect',
  '400': 'Bad Request',
  '401': 'Unauthorized',
  '402': 'Payment Required',
  '403': 'Forbidden',
  '404': 'Not Found',
  '405': 'Method Not Allowed',
  '406': 'Not Acceptable',
  '407': 'Proxy Authentication Required',
  '408': 'Request Time-out',
  '409': 'Conflict',
  '410': 'Gone',
  '411': 'Length Required',
  '412': 'Precondition Failed',
  '413': 'Request Entity Too Large',
  '414': 'Request-URI Too Large',
  '415': 'Unsupported Media Type',
  '416': 'Requested Range Not Satisfiable',
  '417': 'Expectation Failed',
  '418': 'I\'m a teapot',
  '422': 'Unprocessable Entity',
  '423': 'Locked',
  '424': 'Failed Dependency',
  '425': 'Unordered Collection',
  '426': 'Upgrade Required',
  '428': 'Precondition Required',
  '429': 'Too Many Requests',
  '431': 'Request Header Fields Too Large',
  '500': 'Internal Server Error',
  '501': 'Not Implemented',
  '502': 'Bad Gateway',
  '503': 'Service Unavailable',
  '504': 'Gateway Time-out',
  '505': 'HTTP Version Not Supported',
  '506': 'Variant Also Negotiates',
  '507': 'Insufficient Storage',
  '509': 'Bandwidth Limit Exceeded',
  '510': 'Not Extended',
  '511': 'Network Authentication Required' }

Here by using http object, we get all the status code supported by http module of node.js

Command Prompt
Console Window

> var os = require("os");
undefined
> os
{ endianness: [Function],
  hostname: [Function],
  loadavg: [Function],
  uptime: [Function],
  freemem: [Function],
  totalmem: [Function],
  cpus: [Function],
  type: [Function],
  release: [Function],
  networkInterfaces: [Function],
  arch: [Function],
  platform: [Function],
  tmpdir: [Function],
  tmpDir: [Function],
  getNetworkInterfaces: [Function: deprecated],
  EOL: '\r\n' }
> os.type
[Function]
> os.type();
'Windows_NT'

Here we see contents of os module. Also fetch the type of Operating System we are using, by using type() method supported by OS module.

Read Evaluate Print Loop (REPL): Node.js

[youtube https://www.youtube.com/watch?v=F2tYaJADVos]

YouTube Link: https://www.youtube.com/watch?v=F2tYaJADVos [Watch the Video In Full Screen.]

Note: Node.js is built on the same Google’s V8 JavaScript Engine which is using by Google’s Chrome – thus providing the same speed and robustness to our node.js applications.

For quick reference: Status Code and it’s meaning
‘100’: ‘Continue’,
‘101’: ‘Switching Protocols’,
‘102’: ‘Processing’,
‘200’: ‘OK’,
‘201’: ‘Created’,
‘202’: ‘Accepted’,
‘203’: ‘Non-Authoritative Information’,
‘204’: ‘No Content’,
‘205’: ‘Reset Content’,
‘206’: ‘Partial Content’,
‘207’: ‘Multi-Status’,
‘300’: ‘Multiple Choices’,
‘301’: ‘Moved Permanently’,
‘302’: ‘Moved Temporarily’,
‘303’: ‘See Other’,
‘304’: ‘Not Modified’,
‘305’: ‘Use Proxy’,
‘307’: ‘Temporary Redirect’,
‘400’: ‘Bad Request’,
‘401’: ‘Unauthorized’,
‘402’: ‘Payment Required’,
‘403’: ‘Forbidden’,
‘404’: ‘Not Found’,
‘405’: ‘Method Not Allowed’,
‘406’: ‘Not Acceptable’,
‘407’: ‘Proxy Authentication Required’,
‘408’: ‘Request Time-out’,
‘409’: ‘Conflict’,
‘410’: ‘Gone’,
‘411’: ‘Length Required’,
‘412’: ‘Precondition Failed’,
‘413’: ‘Request Entity Too Large’,
‘414’: ‘Request-URI Too Large’,
‘415’: ‘Unsupported Media Type’,
‘416’: ‘Requested Range Not Satisfiable’,
‘417’: ‘Expectation Failed’,
‘418’: ‘I\’m a teapot’,
‘422’: ‘Unprocessable Entity’,
‘423’: ‘Locked’,
‘424’: ‘Failed Dependency’,
‘425’: ‘Unordered Collection’,
‘426’: ‘Upgrade Required’,
‘428’: ‘Precondition Required’,
‘429’: ‘Too Many Requests’,
‘431’: ‘Request Header Fields Too Large’,
‘500’: ‘Internal Server Error’,
‘501’: ‘Not Implemented’,
‘502’: ‘Bad Gateway’,
‘503’: ‘Service Unavailable’,
‘504’: ‘Gateway Time-out’,
‘505’: ‘HTTP Version Not Supported’,
‘506’: ‘Variant Also Negotiates’,
‘507’: ‘Insufficient Storage’,
‘509’: ‘Bandwidth Limit Exceeded’,
‘510’: ‘Not Extended’,
‘511’: ‘Network Authentication Required’