coffeescript-notes.md

CoffeeScript notes

To act as an aide-mémoire and to help explain to others why particular things work (or do not work) I have compiled a list of my coffeescript learnings.

Class properties and instance properties

If you set a property outside of a method CS will treat it like a constant. Take the following as an example, regardless passing a value to the set method, @current will continue to be null:

class Servers
  @current = null
  constructor: ->
    
  set: (value) ->
    @current = value

  get: ->
    @current    

To correct this, change to the following:

class Servers  
  constructor: ->
    @current = null

  set: (value) ->
    @current = value

  get: ->
    @current    

I believe any variable starting with @ outside of the scope of a method acts as an equivalent static type in c#

So if you have a class like:

class Servers
  @current = 123
  constructor: ->    

then without instantiation you'll get:

console.log Servers.current

123

Chutzpuh & VS

The path to any references must be relative otherwise Chutzpuh will not find it. For instance, the following will throw an ReferenceError: Can't find variable: TimeOut in error:

## <reference path="/vendor/jasmine-1.3.1/jasmine.js" />
## <reference path="/scripts/models/timeout.js" />

describe "Timeout suite", ->
    it "initalise Timeout object", ->
        timeout = new TimeOut

When I add ../.. to the path all is good:

## <reference path="../../vendor/jasmine-1.3.1/jasmine.js" />
## <reference path="../../scripts/models/timeout.js" />

describe "Timeout suite", ->
    it "initalise Timeout object", ->
        timeout = new TimeOut

Callbacks

Whenever you pass a function to a class that is to act as a callback, that function much be called with parenthesis if no parameters are required. For example:

MyClass = class MyClass
	constructor: (@callback) ->
	doSomething: ->
		@callback()

myCallback = ->
	alert 'Hi'
	
myClass = new MyClass myCallback

You will note that the callback @callback() has '()'. Without these, the callback function will not be called.

Arrays of objects

When using arrays, the , separator much be an indention back from the object itself. This is illustrated below:

myArray = [
		{id: "1", name: "abc"}
	,
		{id: "1", name: "xyz"}
]

Call a method from within a class

To call an method you much either use @ or this. notation. For example:

MyClass = class MyClass
	constructor: ->
		@doSomething()
		this.doAnotherSomething()
	doSomething: ->
	doAnotherSomething: ->
		

If you omit the prefix the method will not get called.

Lost scope via callback or attaching to different object

Here I have included a snippet from a class. Please take note of the _assess method. You will see a fat arrow => being used. I have used this here as the method is being attached to another / different object - in the _start method - and such the scope for the container class is lost. To avoid this, we used a fat arrow. If we use a thin arrow -> instead, the class properties @minutes, @period, @interval & @timedOut would not be accessible:

...
	_start: ->
		@internval = setInterval this._assess, @interval        

    _assess: =>                
        @minutes = @minutes + 1 if @minutes < @period
        if @minutes > @period            
            @internval = clearInterval @internval
            @timedOut() 

Testing

Useful links:

Jasmine - http://pivotal.github.io/jasmine/
Jasmine-jquery - https://github.com/velesin/jasmine-jquery
Chutzpah - http://chutzpah.codeplex.com/

Testing where time is a factor

Whenever you need to test a feature that involves a time delay then you can use the Clock object in jasmine jasmine.Clock.useMock()

To illustrate this I have included an example below:

describe "Timeout suite", ->   

 	flag  = false   
    restartFlag = false     
    timeout = null
    callback = ->
        flag = true
    restartCallback = ->
        restartFlag = true

    beforeEach ->
        timeout = new TimeOut 2, 2000, callback, restartCallback    

    it "restart called and callback triggered after a minute", ->   
        jasmine.Clock.useMock();
        timeout.start()
        timeout.restart()
        jasmine.Clock.tick(2100)
        timeout.restart()
                
        (expect restartFlag).toBeTruthy()        
        (expect timeout.internalBeenMoreThanAMinute).toBeFalsy()

In the sample above a callback restartCallback - is called after a specific amount of time. I know that 2+ seconds is enough time to wait and that the callback should have been called by then. The restartCallback assigns true to the variable restartFlag. It is this variable's value I am evaluating in the assertion.

Testing files with dependency

There are situations where a number of tests may depend on other files, the way to reference these files is: (This solution refers to coffeescript with Visual Studio and chutzpah as test runner.)

###
/// <reference path="../code/calculator.coffee" / >
###