CoffeeScript, An Introduction for Nodejs developers

1. |
COFFEESCRIPT
AN INTRODUCTION FOR NODE DEVELOPERS
BY: MEHDI VALIKHANI
SOFTWARE ENGINEER @ ALPHATISE
Follow me: @[email protected]

2. IT'S JUST JAVASCRIPT
COFFEESCRIPT IS A PROGRAMMING LANGUAGE THAT
TRANSCOMPILES TO JAVASCRIPT.
SYNTACTIC SUGAR TO JAVASCRIPT

3. IT'S MATURE AND PRODUCTION-READY
DEVELOPED BY: JEREMY ASHKENAS
INITIAL COMMIT: DECEMBER 13TH, 2009
FIRST RELEASE: DECEMBER 24H, 2009
VERSION 1.0: FEBRUARY 2010
CURRENT VERSION: 1.8

4. WHO'S USING
COFFEESCRIPT?
DROPBOX
GITHUB

5. WRITE LESS, DO MORE
HUMAN-READABLE CODE
STAY AWAY FROM WEIRD JS BEHAVIOUR
SAY GOODBYE TO PROTOTYPE! USE CLASSES
ANY MANY MORE ...

6. COFFEESCRIPT SYNTAX

7. NO MORE VAR ; ( )

async = require 'async'
console.log async.VERSION



var async = require('async');
console.log(async.VERSION);

8. FUNCTIONS
IT'S PART OF OUR EVERYDAY LIFE IN JS WORLD
LET'S BE AGILE!

9. addUser = (user, cb) ->
model = new User
#DO SOMETHING
model.save (err, result) ->
cb null, result



var addUser = function(user, cb) {
var model = new User();
//DO SOMETHING
model.save(function(err, result){
cb(err, result);
});
}

10. IMPLICIT RETURN

someFunction = (param1, param2) ->
param1 * param2 * param2
console.log someFunction 100, 200



var someFunction;
someFunction = function(param1, param2) {
return param1 * param2 * param2;
}
console.log(someFunction(100, 200));

11. OBJECTS
GET RID OF THOSE { } ,

bus =
routeNumber: 273
from: 'Wynyard'
to: 'Chatswood'
via: 'North Sydney, Pacific Highway'



var bus = {
routerNumber: 273,
from: 'Wynyad',
to: 'Chatswood',
via: 'North Sydney, Pacific Highway'
}

12. query =
status:
$in: ['active', 'pending_for_approval']
payment:
$nin: ['invoice', 'free']
tc:
$exists: true



var query = {
status: {
$in: ['active', 'pending_for_approval']
},
payment: {
$nin: ['invoice', 'free']
},
tc: {
$exists: true
}
}

13. STRING INTERPOLOATION

meetup = 'Node'
msg = "#{meetup} meeup is awsome!"
console.log msg


var meetup = 'Node';
var msg = meetup + ' meetup is awsome!';
console.log(msg);

14. CLASSES
BETTER INHERITANCE WITHOUT PROTOTYPE
WE SHOULDN'T USE LIBRARIES TO HAVE CLASSES IN JS

15. class Cache
generateCacheKey: (key) ->
throw new Error 'Not Implemented'
getPeriod: ->
120 * 60
store: (key, data) ->
throw new Error 'Not Implemented'
clearCache: (key) ->
#DO SOMETHING
class RedisCache extends Cache
generateCacheKey: (key) ->
"redis_cache_#{key}"
store: (key, data) ->
period = @.getPeriod()
#STORE IN REDIS

16. DESTRUCTURING OBJECTS

{Router} = require 'express'
router = new Router



var express = require('express');
var Router = experss.Router;
router = new Router();

17. DESTRUCTURING ARRAYS

student = 'Mehdi Valikhani'
[firstName, lastName] = student.split ' '



var student, ref, firstName, lastName;
student = 'Mehdi Valikhani';
ref = student.split(' ');
firstName = ref[0];
lastName = ref[1];

18. DESTRUCTING ARGUMENTS

calculator = ({width, height}) ->
width * height
options =
width: 10
height: 5
alert calculator options

19. EXISTENTIAL OPERATOR ?
REMOVE THOSE NULL OR UNDEFINED CHECKES FROM CODE

if err?
#log to logger
cb err



if (typeof err !== "undefined" && err !== null)
//log to logger
cb(err);

20. INSTALL COFFEESCRIPT
npm install -g coffee-script

21. EXECUTE A SCRIPT
coffee /path/to/script.coffee

22. COMPILE A SCRIPT
coffee -c /path/to/script.coffee

23. NODE + COFFEE
FROM SCRATCH
REST API DEVELOPMENT USING EXPRESS + NODE + COFFEE

24. CODE STRUCTURE

+ lib
+ books
Book.coffee //Our Mongoose Model
router.coffee //router for books API
+ node_modules
+ body-parser //from JSON responses
+ coffee-script //compiler of Coffee files
+ express //express framework
app.coffee //express app config
package.json // NO DESCRIPTION
index.js //ACTUAL MAGIC HAPPENS HERE!

25. app.coffee

bodyParser = require 'body-parser'
express = require 'express'
userRouter = require './lib/books/router'
app = express()
app.use bodyParser.json()
app.use '/users', userRouter
module.exports = app

26. lib/books/router.coffee

{Router} = require 'express'
Book = require './Book'
router = new Router
fetchBook = (req, res, next) ->
req.paramBook = Book
next()
getBook = (req, res) ->
res.json(req.paramBook)
router.route('/:book_id')
.all(fetchBook)
.get(getBook)
module.exports = router

27. index.js

require('coffee-script/register');
var app = require('./app');
app.listen(1984, function(){
console.log('App is available via http://127.0.0.1:1984');
});

28. RUN THE APP
node index.js
nodemon -e js,coffee index.js

29. NODE + COFFEE
AN EXISTING PROJECT

30. ADD FOLLOWING CODE TO YOUR STARTER FILE
require('coffee-script/regiter');

31. THAT'S IT!
Add .coffee files, write your code in coffee
require other .js or .coffee files as always

32. RUN THE APP
node index.js
nodemon -e js,coffee index.js

33. DEBUGGING
COFFEESCRIPT
APPLICATIONS

34. USE "DEBUGGER" AS ALWAYS

fetchBook = (req, res, next) ->
debugger
req.paramBook = Book
next()


node debug index.js

35. BUT DON'T FORGET!
in debug mode, you will be faced with compiled
JS code

break in lib/books/router.coffee:11
9
10 fetchBook = function(req, res, next) {
11 debugger;
12 req.paramBook = Book;
13 return next();
debug> repl
Press Ctrl + C to leave debug repl
> req.params.book_id
'123'
>

36. JAVASCRIPT SCOPING
in JavaScript, the scope of a variable is
defined by its location within the source code
(it is apparent lexically) and nested
functions have access to variables declared in
their outer scope. - mozilla.org

37. Question: What's result of running this code?

name = 'Alex'
greeting = ->
name = 'James'
console.log "Hey #{name}!"
greeting()
console.log "Hey #{name}!"

38. A:
> Hey James!
> Hey James!
B:
> Hey James!
> Hey Alex!

39. "A" IS CORRECT ANSWER
> Hey James!
> Hey James!

40. THIS IS COMPILED-TO-JS VERSION OF ABOVE
CODE

var greeting, name;
name = 'Alex';
greeting = function() {
name = 'James';
return console.log("Hey " + name + "!");
};
greeting();
console.log("Hey " + name + "!");

41. TWO IMPORTANT FACTS
ABOUT COFEESCRIPT SCOPING
Variable shadowing is not allowed
variable is created at the moment of the first assignment to it

42. "VARIABLE SHADOWING IS NOT ALLOWED"
DOESN'T MEAN
YOU CAN'T DEFINE A VARIABLE MORE THAN
ONCE IN DIFFERENT FILES
IT MEANS
YOU CAN'T DEFINE IT MORE THAN ONCE IN A
SINGLE FILE

43. SO WHAT SHOULD I DO IF I WANT TO HAVE
SHADOWS?
It's not a good practice, don't do that!
It decreases readbility of your code!
Brings more confusion to your code
With shadowing you can't access our variables anymore (with
same name)

44. USE `` TO BRING VAR BACK

name = 'Alex'
greeting = ->
` `
name = 'James'
console.log "Hey #{name}!"
greeting()
console.log "Hey #{name}!"

var name
It a kind of hack! Don't do that!

45. SHADOW IT USING FUNCTION PARAMETER

name = 'Alex'
greeting = (name = '')->
name = 'James'
console.log "Hey #{name}!"
greeting()
console.log "Hey #{name}!"


Better first solution!

46. USE COFEESCRIPT'S CLOSURE FEATURE
This is much much better!

name = 'Alex'
greeting = ->
do (name = '') ->
name = 'James'
console.log "Hey #{name}!"
greeting()
console.log "Hey #{name}!"

47. MORE INFO ABOUT LEXICAL SCOPING:
https://github.com/raganwald-
deprecated/homoiconic/blob/master/2012/09/actually-YOU-
dont-understand-lexical-scope.md
https://github.com/raganwald-
deprecated/homoiconic/blob/master/2012/09/lexical-scope-
in-coffeescript.md

48. USEFUL RESOURCES
Your best friend
Don't translate CoffeeScript to JS, try to learn as new langage
Teaches CoffeeScript as new language instrad of translating to
JS
Best Practices
CoffeeScript Docs
CoffeeConsole: A Google Chrome Extention
CoffeeScript Ristretto
The Little Book On CoffeeScript
CoffeeScript Style Guide

49. Thank you!