Published: Aug 11, 2018 Tags: web, backend Category: Engineering

Recently, I used Node.js quite a lot to handle personal projects. It is easy to start, and also easy to get wrong. This blog covers the basics part of Node.js development.

Module

Require

Every module in node is singleton.

Use require to use module, the following is the search sequence of require method:

• First find js file
• Then json file
• Then node file

If the module name is index.js, then it is okay just write directory name in the require parameter.

require() can inject objects for dependency injection.

Module exports

From the modele itself, use exports keyword to make properties and methods available outside of the module file.

1	exports.myDateTime = function () {
2	    return Date();
3	};

Http module

http module can be used to write header or content. See following example:

1var http = require('http');
2http.createServer(function (req, res) {
3  res.writeHead(200, {'Content-Type': 'text/html'});
4  res.write('Hello World!');
5res.write(req.url); // read query string
6  res.end();
7}).listen(8080);

File module

File module can be used for file system operation.

 1require(fs)
 2var http = require('http');
 3var fs = require('fs');
 4http.createServer(function (req, res) {
 5  fs.readFile('demofile1.html', function(err, data) {
 6    res.writeHead(200, {'Content-Type': 'text/html'});
 7    res.write(data);
 8    res.end();
 9  });
10}).listen(8080);

Other useful methods in file module.

write file: fs.appendfile(), fs.open(), fs.writefile()

delete file: fs.unlink()

rename: fs.rename()

Url module

Url module can be used to parse various parts of url.

 1url.parse('https://www.pluralsight.com/search?q=buna')
 2
 3Url {
 4protocol: 'https:',
 5slashes: true,
 6auth: null,
 7host: 'www.pluralsight.com',
 8port: null,
 9hostname: 'www.pluralsight.com',
10hash: null,
11search: '?q=buna',
12query: 'q=buna',
13pathname: '/search',
14path: '/search?q=buna',
15href: 'https://www.pluralsight.com/search?q=buna' }

example

1http.createServer(function (req, res) {
2  res.writeHead(200, {'Content-Type': 'text/html'});
3  var q = url.parse(req.url, true).query;
4  var txt = q.year + " " + q.month;
5  res.send(txt);
6}).listen(8080);

Use the url for testing: http://localhost:8080/?year=2017&month=July Output is: 2017 July

Event model

The event model of node.js is asymmetric. The core part is event loop.

For example, here is how Node.js handles a file request:

• Sends the task to the computer's file system.
• Ready to handle the next request.
• When the file system has opened and read the file, the server returns the content to the client.

The event loop looks like this:

• The entity that handles external events and converts them into callback invocations
• A loop that picks events from the event queue and pushes their callbacks to the call back stack
• Node will process the event queue when call stack is empty

There are three methods look quite similar, it will be good to understand the difference:

• setTimeout
• setImmediate
• Process.nextTick (not relevant event loop)

NPM

Npm is node package manager, which is the core part of javascript ecosystem.

Commands

Npm start, npm test: will run when there is start/test script in the package.json

Npm -h: to show the help

Npm help: can open a browser

Npm init: will create the package.json

Npm list: list all installed packages

Npm can install global package, and can also install in local repository

Npm can specify the versions when using npm i

Npm can specify environment, e.g. --save, --prod, --dev

NPM can choose install from 'gist' instead of a version, also can install from folder

npm publish: can publish your package to npm registery

Version

Semantic version: major.minor.patch

• Patch increase when bug fixing
• Minor increase when introduce new feature
• Major increase when breaking changes

In the package.json: ^means major version can be greater, ~means minor version can be greater

npm version patch/minor/major to update the version info in the pcakge.json rather than manually change the version (it will also do the git commit for developers)

Others

Difference from client javascript

Javascript in node.js app, differentiate client and server code.

For example:

• server can call require while client can call windows.
• server code modification needs to restart node to see the changes, while client code just need browser refresh.
• console.log in the server code will output the message to terminal app, the client code will output the message the browser console.

Uglify

gulp can uglify your repository

Error code

If there is error, can use res.status(500).send(err) to return the error code

1bookRouter.route('/Books/:bookId').get(function(req, res)) {
2    Book.findById(req.params.bookId, function(err, book) {
3        if (err) {
4            res.status(500).send(err);
5        } else {
6            res.json(book);
7        }
8    })
9}

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Written by Binwei@Singapore