Inheritence the Node.js way with

Typically in Javascript for inheritance you would use ether the prototype pattern or used the Object.create() passing it a prototype to inherit from.
In the prototypical patter you compose a constructors prototype object from the inherited classes (constructors) creating the __proto__ chain.
Object.create does the same but in a cleaner simpler way.

In node there's a way to avoid messing around with creating Constructor.prototype instances from other constructors and thus creating the __proto__ chain, its called the inherits function of a the core module util that we discussed previously.

The inherits function get two constructors as arguments, on is the parent (super/base class) the second is the inheriting constructor.
By calling the function with the desired parameters, the Parent class's prototype property will be mutated to inherit the super class prototype.
Example:
inherits(Bird, Animal);

Another thing to note is:
In order to inherit own properties on the super class the inheriting class should call the constructor inside its activation scope. example:
Bird() {
Object.call(Animal)
}

EventEmitter
events.EventEmitter:
example:

Combining EventEmitter with Node's inherit function

Inheriting from EventEmitter into your Constructor can be usefull to export an events api for your module.
Many modules build their events by inheriting from EventEmitter.
Example:
var utils_inherit = require('utils').inherit;
var Emitter = require('events').EventEmitter;
function Animal() {
Object.call(Emitter)
}
utils_inherit(Animal, Emitter)
// Animal now inherited Emitter fully
Animal.prototype.startWalking = function(distance){
this.emit('walking',['animal'])';
}
var animal = new Animal();
animal.on('walking',function(data){
console.log('animal is walking, and will stop after '+data+'meters');
});
animal.startWalking(2000)

process events you can listen to

the node process object inherits from EventEmitter and can be listened to on events it's emitting.
example:
process.on('uncaughtException', function (err) {
      console.log('Caught exception: ', err);
      console.log('Stack:', err.stack);
      process.exit(1);
});

Some events you can listen to on process

uncaughtException - raised internal error
exit - on exiting the process, no async operations can be done at this point since the process has already been tared down.
SIGINT - emitted when the user presses Ctrl+C when a process is executing in the CLI

Streams

Streams are good for transferring large file from one locations to the other, this is because unlike a buffer streams do not wait until all the data is converted to the desired format, but instead they transfer the data by chunks.
This way the side that requested the data can almost immediately start doing something with the data, like starting to render an image before all image is recieved, or star playing a video before all video was received.

NOTE! Since streams are also event driven, they also inherit from EventEmitter, and have the emit & on methods

There are 4 main types of streams:

Readable - stream that can only be read
Writable - streams that can only written to
Duplex - streams that can be both readable & writable
Transform - streams that need to do some procedure on the received data before transporting it, for example encryption or compressing.

These classes can be found under the 'streams' core module (see Important Core Modules).

NOTE! Two noteworthy streams in node are process.stdin & process.stdout

example for creating streams from objects:
var stream = require('streams');
var readable = new stream.Readable({something:'something'});
var writable = new stream.Writable({something:'something'});

Pipes

Streams can also be piped, which means that you can for example take a read-only-stream & pipe it to a write-only-stream.
Take the simple scenario for example of serving a text file to the client.
the text file can be a read-only-stream and be pipe to the process.stdout which is a write only stream.
To create streams from files you can use the fs modules createReadStream method, and to pipe them into the process.stdout can be as simple as the following few lines:

var fs = require('fs');
var readableStream = fs.createReadStream('./cool.txt');
readableStream.pipe(process.stdout);

Pipes can also be chained for further processing of the data-chunks, for example if you want to serve a text file and zip (using a community module called zlib) it before sending it:

var fs = require('fs');
var gzip = require('zlib').createGzip(); // gzip midleware
var readableStream = fs.createReadStream('./cool.txt');
var readWriteStream = fs.createDuplexStream('./cool.txt.gz');
// the chaining
readableStream.pipe(gzip).pipe(writeableStream).pipe(process.stdout);

Writing to writeable streams

You can define a file as a writable stream, and for example inside a loop write into the file, then when loop ends call the .end method.
example:

var fs = require('fs');
var writableStream = fs.createWriteStream('message.txt');
var words = ['hello', 'stream','world'];
for (let i = 0; i < words.length; i++) {
writableStream.write(words[i]+' ');
}
writableStream.end(' .');
// file contents is now: hello stream world .

Nächster

Vorher

Node - Performance

Beschreibung