Node.js: CAMTA Presentation

MUMPS is dead? Rob Tweed M/Gateway Developments Ltd http://www.mgateway.com Twitter: @rtweed

What is Node.js?

What is Node.js? … so what does that mean?

What is Node.js?

What is Node.js?
Node.js is a server-side JavaScript environment.

What is Node.js?
Node.js is a server-side JavaScript environment.
Node.js is a server-side JavaScript interpreter that allows us to handle and make requests via JavaScript:
In a web or networked environment

Just Javascript Browsers Node.js server process Javascript Javascript Database

So instead of this: http/ https Persistent connections Browser Browser Browser Web Server (Apache/ IIS) CSP Caché CSP interface Caché CSP interface Your scripts Your data EWD CSP pages

You'd have something like this: Browser Browser Browser Cach é http/ https WebLink interface Cach é CSP interface Child_process connections EWD Runtime Your scripts Your data EWD routines Node.js process Javascript Web server & request/response Handling logic stdin/stdout GT.M or Cach é

What is Node.js?

V8
Node.js uses the Google V8 engine to provide the Javascript environment
V8 is the engine in the Chrome browser
V8 is very fast!

What is Node.js?

What is Node.js?
Node.js is a server-side JavaScript environment that uses an asynchronous event-driven model .

What is Node.js?
Node.js is a server-side JavaScript environment that uses an asynchronous event-driven model .
No threads
Node.js runs in a single process, handling all client requests
Non-blocking I/O
Can't wait for slow resources to respond
Files, databases, etc
Must not block the process or everyone waits

Asynchronous I/O & Javascript
Javascript is an ideal language for this
No I/O in a browser
Access to remote resources is asynchronous
The A in Ajax!
Send a request for a resource and define a handler to deal with it when it arrives
"Call-back function"

Asynchronous I/O & Javascript
On the server, in Node.js:
Make a request for I/O (file/ database)
Define a call-back function
Move on immediately
When the I/O is complete:
Call-back function is fired to handle it

Asynchronous I/O & Javascript Synchronous read from a file in MUMPS: set file = "mydata.txt" open file:"r" use file read buffer // do something with the buffer contents … . // then move on to the next task

Asynchronous I/O & Javascript Synchronous read from a file in MUMPS: set file = "mydata.txt" open file:"r" use file read buffer // do something with the buffer contents … .// at this point the thread is blocked … .// until the buffer contents are read from the file // then move on to the next task

Asynchronous I/O & Javascript The Asynchronous way in Javascript: var fs = require('fs'); fs.readFile('mydata.txt', function (err, buffer) { // Do something with the data in the buffer }); // Immediately execute the next statements // while it waits for I/O

What is Node.js?

Node.js Evented I/O
Node.js is a single process running an event loop
When an event occurs, fire a call-back function to handle it
When no events are coming in, the Node.js process sits in a dormant state

Node.js process
A Node.js process can handle many thousands of clients
Provided none of them block
Provided none of them do CPU-intensive processing

Node.js / Javascript: popularity
Node.js is now the most followed project on Github, exceeding Ruby on Rails
Javascript is now the most popular language in the world, based on a number of measures including number of Github projects

Significance for GT.M & Cach é
Opportunity to use Javascript as a primary scripting language
Global storage for Javascript
JSON / Global mapping

Why Javascript?
The world's most popular language
The world's sexiest, coolest server-side environment
Javascript's dynamic interpreted nature has many similarities to MUMPS

Why not MUMPS?
Rightly or wrongly, the perception in the mainstream is that the MUMPS language is old-fashioned and inherently broken
Daily WTF article:
http://thedailywtf.com/Articles/A_Case_of_the_MUMPS.aspx
Yet global storage has a great deal to offer as a NoSQL database technology
Result: the benefits and advantages of global storage are ignored because modern developers will refuse to learn the language

Making Global Storage Attractive
Make it accessible via the coolest, sexiest, most popular language on the planet
Demonstrate that global storage is a great NoSQL technology
"Universal NoSQL Engine"
http://www.mgateway.com/docs/universalNoSQL.pdf

Downside of Node.js
Asynchronous programming
Callback hell!
Deeply nested call-backs
Complexity of logic
Essential to understand closures
2 main types:
Dependent
Concurrent
Care needed when using for loops to invoke logic that includes callbacks

Dependent callbacks myFunc1(inputs, function(error, results) { var value = results.value; // myFunc2 can't run until myFunc1 returns its results myFunc2(value, function(error, results) { var myResult = results.value; }); });

Concurrent callbacks var count = 0; myFunc1(inputs, function(error, results) { count++; if (count === 3) myFunc4(inputs); }); myFunc2(inputs, function(error, results) { count++; if (count === 3) myFunc4(inputs); }); myFunc3(inputs, function(error, results) { count++; if (count === 3) myFunc4(inputs); }); // myFunc isn't invoked until all 3 functions are complete // Uses the properties of closures to allow count to be incremented by // the callbacks in the three functions

Closures
Inner functions have access to the outer function's variables, even after the outer function has completed

Closures
Inner functions have access to the outer function's variables, even after the outer function has completed
var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; }; var test = digit_name(); // test is a function that takes a value var text = test(3); console.log("text = " + text);

Closures
Could be rewritten to use a self-executing function as follows
var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; } () ; // digit_name is the result of running the outer function, // so it's a function that takes a value var name = digit_name(3); // name will be 'three'

Downside of Node.js
Asynchronous programming
Database access functions can't return a value
Value is embedded inside the callback
Can't chain database functions as objects:
document.getElementById('x').parent.firstChild.tagName

Accessing globals from Node.js
Cache & GT.M:
https://github.com/robtweed/ewdGateway
Complete webserver + gateway for EWD
Also includes global access functions, eg:
get
set
getJSON
mFunction

Node.js: CAMTA Presentation

by Rob Tweed on Dec 09, 2011

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Node.js: CAMTA Presentation — Presentation Transcript