This question already has an answer here:
Static classes and methods in coffeescript
(1 answer)
Closed 8 years ago.
I cant understand exactly what # (this) does infront of class functions. I am using Spine framework, and I got a class Contact which extends Spine.model. I override the Spine methods for creating, deleting, fetching etc, and have them print on the console first like this:
create: ->
console.log('create')
super
destroy: ->
console.log("destroy")
super
Some of these methods will work the same if I add # infront, for example create, while others will not work without #, and others will not work with #. All the methods I override can be seen on the link above.
Is it possible to explain me the effect of # symbol infront of
functions, and why its causing this behaviour?
Answer from mu is too short :
You can define class methods by prefixing them with #:
class Box2DUtility
constructor: () ->
#drawWorld: (world, context) -> alert 'World drawn!
'
And then draw your world...
Box2DUtility.drawWorld()
Demo: http://jsfiddle.net/ambiguous/5yPh7/
And if you want your drawWorld to act like a constructor then you can say new # like this:
class Box2DUtility
constructor: (s) -> #s = s
m: () -> alert "instance method called: #{#s}"
#drawWorld: (s) -> new # s
Box2DUtility.drawWorld('pancakes').m()
Demo: http://jsfiddle.net/ambiguous/bjPds/1/
Related
I'm trying to define a helper method in konacha in coffeescript, something like this
#expect_int_is_universal = (i) ->
expect(i).to.equal 42
describe '#test', ->
it 'checks if integer is 42', ->
#expect_int_is_universal(42)
Is it possible in konacha?
edit: error log here:
update: the fix is putting it inside a beforeEach block
beforeEach ->
#expect_int_is_universal = (i) ->
expect(i).to.equal 42
describe '#test', ->
it 'checks if integer is 42', ->
#expect_int_is_universal(42)
mu is too short hasn't successfully converted his comment as the answer, but i'll provide it here below:
# (AKA this) inside your it callback is not the same # as at the top level so you're defining expect_int_is_universal as a method on one object but trying to call it as a method on another object. Try without the #s. I don't know enough Konocha, Mocha, or Chai to say any more than that
While learning coffeescript, I'm trying to create an instance of class A inside a method of class B, this is the code:
class #A
constructor: (#x) ->
show: ->
alert #x
class #B
constructor: (#y) ->
show: ->
a = new #A("eric")
alert a.x
alert #y
b = new #B("daniel")
b.show()
the error is TypeError: undefined is not a function.
Any help is appreciated.
Thanks
You have two problems:
# is just another way of saying this in CoffeeScript. That's all it means.
Classes are (more or less) just variables or properties like any other in CoffeeScript.
So when you say #A, you're just looking for the A property of this and your show is really saying:
a = new this.A("eric")
In that context, # will be an instance of B and Bs don't have A properties. Instead you should just say:
a = new A('eric')
Using # when defining a class:
class #A
#...
is just a way to make a class globally available. At the top level, # will (almost always) be window in a browser so you're really saying:
class window.A
#...
and window properties are globals. Keep in mind that each CoffeeScript file is wrapped in a function when it is converted to JavaScript:
Although suppressed within this documentation for clarity, all CoffeeScript output is wrapped in an anonymous function: (function(){ ... })(); This safety wrapper, combined with the automatic generation of the var keyword, make it exceedingly difficult to pollute the global namespace by accident.
So if you just said:
class A
then A would only be available to other code in that file. Saying:
class #A
makes A global.
If you're only working with one file then you don't need the #s on your classes:
class A
constructor: (#x) ->
show: ->
alert #x
class B
constructor: (#y) ->
show: ->
a = new A("eric")
alert a.x
alert #y
b = new B("daniel")
b.show()
Don't get in the habit of prefixing everything with #, only use it on classes when you need it and you know exactly what it will do. Even when you need it, there are better ways: use require.js to manage your dependencies, use an global application-specific object to manage scopes, ...
I want to join (use) classe in Coffescript files, and i found some usefull ideas here (sry for not including all links), since none fitted my needs (at least not as i like) I tried to find an own solution, this will work fine, but is there something I have overseen?
following "base" and "base class" are not OO words, I just did not find better names
I have a base (class) file TechDraw
class TechDraw
constructor: ->
$(window).load () =>
... do somthing
wave_to_me: ->
say 'I wave' # say is a basic func, I always use for debugging (console.log)
#TechDraw = new TechDraw
this works fine
Now I want to expand/extend my class with "sub classes/modules" in other files; ie. I have a TechDrawLine, and a TechDrawCalc, ans so on
What I did, was building a coffee file for each of them like:
class TechDrawConnector
constructor: (p)->
#parent=p
wave: (msg) ->
say 'yes its me, the connector:',msg
`window.TechDrawConnector = function(p) { return new TechDrawConnector(p) };`
# the last instead of a simple new like
# #TechDrawConnector = new TechDrawConnector
and my base(ic) class/module I extendet like this:
class TechDraw
constructor: ->
$(window).load () =>
#Connector=window.TechDrawConnector(this)
#LineGuy=window.TechDrawLineGuy(this)
#Connector.wave('init')
Since I am a newbee in coffeescript (yes javascript also) my solution feels to simple ...
Have I overseen somthing? The Polution of the global namespace is not so bad I think
You cant create an "extension" that way.
If you define the same class in the same namespace a second time the first class will simply be overwritten and become in accessible. This will mostly be dependent on the order of loading of the compiled JavaScript files.
However you could either later add an method to the prototype of the class
#file a.coffee
class A
constructor: ->
#foo()
#file B.coffee
A::foo = -> #do something
However this is no good style and can certainly be very confusing some time and lead to brittle errors.
Better would be to use a form of dependency injection
#file a.coffee
class A
constructor: (#closure) ->
$(window).load () => #closure()
#file B.coffee
new A () ->
#Connector=window.TechDrawConnector(#)
#LineGuy=window.TechDrawLineGuy(#)
#Connector.wave('init')
Hi I'm new to Js and Coffeescript, here's a situation I feel difficult to refer the property of parent object which is App in the following example
App =
init: ->
this.foo = 'bar'
this.bindEvent()
bindEvent: ->
$('#test').click(this.show)
show: ->
alert this.foo
App.init()
I think the fat arrow may do the trick but once I've changed to show: =>, this in the context of show method refers to the window object, instead of App object that I want to
. Anybody can tell me how to do it right?
http://jsfiddle.net/kZpHX/
When you define your show function, # (AKA this) actually is window so
show: => console.log(#)
will bind show to window. The problem is that you're simply defining an object so there isn't anything to bind to: you aren't defining a class so this is window. You could refer to App explicitly like this:
App =
#...
show: -> alert(App.foo)
Demo: http://jsfiddle.net/ambiguous/3sRVh/
The this.foo in init will do the right thing because saying App.init() sets up the expected this.
You could also hook up the desired this manually:
bindEvent: ->
$('#test').click => #show()
# or
bindEvent: ->
_this = # # JavaScript style
$('#test').click -> _this.show()
Demos: http://jsfiddle.net/ambiguous/byL45/, http://jsfiddle.net/ambiguous/MT8fG/
Or you could create a class for your App instead:
class App
constructor: ->
#foo = 'bar'
#bindEvent()
bindEvent: ->
$('#test').click(#show)
show: =>
console.log(#foo)
new App
That way your show: => will behave the way you expect it to.
Demo: http://jsfiddle.net/ambiguous/byatH/
I come from a C#/Java background which use a class based OO system and I don't get the JavaScript/CoffeeScript prototype OO system yet. I've written a CoffeeScript class below which allows me to display names for contacts according to a system-side preference. I can only get the class to work by making the joinNonEmpty(stringList, joinText) method belong to the prototype and calling it the way I would call a static method in Java/C# land.
Is there a way I can make this method call using this.joinNonEmpty(...)?
Can you shed some light on why I can reference the firstLastRender, lastFirstRender and firstOrNickThenLast methods in the constructor with this. but it doesn't work from those methods when calling the joinNonEmpty helper?
Does this have something to do with how I'm locating the appropriate method via the preference map?
prefs = displayNameFormat: "FirstOrNickThenLast"
class DisplayNameRenderer
constructor: ->
#prefToRenderMap =
FirstLast: this.firstLastRender
LastFirst: this.lastFirstRender
FirstOrNickThenLast: this.firstOrNickThenLast
# Why does this method have to be static (a class method)?
#joinNonEmpty: (stringList, joinText) ->
nonEmptyStrings = []
for s in stringList
nonEmptyStrings.push(s) if s isnt null and s isnt ""
nonEmptyStrings.join(joinText)
firstLastRender: (contact) ->
# TypeError: Object expected.
joinNonEmpty([contact.firstName, contact.lastName], ' ')
lastFirstRender: (contact) ->
# TypeError: Object doesn't support this method or property
this.joinNonEmpty([contact.lastName, contact.firstName], ', ')
firstOrNickThenLast: (contact) ->
# Works correctly.
DisplayNameRenderer.joinNonEmpty([(if contact.nickname isnt null and contact.nickname isnt "" then contact.nickname else contact.firstName), contact.lastName], ' ')
render: (contact) ->
#prefToRenderMap[prefs.displayNameFormat](contact)
contact = firstName: "Jonathan", nickname: "Jonny", lastName: "Appleseed"
dnr = new DisplayNameRenderer()
# => "Jonny Appleseed"
console.log dnr.render(contact)
Thanks for taking the time to answer.
this (AKA #) is determined when the function is called (with exceptions as below). So when you do this:
#prefToRenderMap =
FirstLast: this.firstLastRender
LastFirst: this.lastFirstRender
FirstOrNickThenLast: this.firstOrNickThenLast
You're storing unbound references to the three functions in the #prefToRenderMap instance variable and #prefToRenderMap is itself an object. Then you try to call the methods in your DisplayNameRenderer instance like this:
#prefToRenderMap[prefs.displayNameFormat](contact)
and everything falls apart because the methods are called in the wrong context and # isn't what they're expecting it to be. If prefs is 'FirstOrNickThenLast' then you're effectively doing this:
#prefToRenderMap.FirstOrNickThenLast(contact)
and # (AKA this) will be #prefToRenderMap inside the firstOrNickThenLast method. But, of course, #prefToRenderMap doesn't have any of the methods that you're trying to call so you get various errors.
One solution is to use the fat arrow (=>) to define the methods:
The fat arrow => can be used to both define a function, and to bind it to the current value of this, right on the spot.
So you could have things like this:
joinNonEmpty: (stringList, joinText) ->
#...
firstLastRender: (contact) =>
#joinNonEmpty([contact.firstName, contact.lastName], ' ')
and everything will work out. Here's a stripped down demo that will also show you your this problem:
http://jsfiddle.net/ambiguous/RAPJw/1/
You could also avoid this problem by referring to the methods by their names. Given a method name in a string, m = 'some_method', you can call that method like this o[m]() in both JavaScript and CoffeeScript and the result will be the same as if you said o.some_method(). A better structure would look more like this:
class DisplayNameRenderer
constructor: ->
#prefToRenderMap =
FirstOrNickThenLast: 'firstOrNickThenLast'
joinNonEmpty: (stringList, joinText) ->
#...
firstOrNickThenLast: (contact) ->
#joinNonEmpty([(if contact.nickname isnt null and contact.nickname isnt "" then contact.nickname else contact.firstName), contact.lastName], ' ')
render: (contact) ->
#[#prefToRenderMap['FirstOrNickThenLast']](contact)
Note the change to the structure of #prefToRenderMap and how it is used in render. And a demo of this approach: http://jsfiddle.net/ambiguous/DFYwu/
As an aside, instead of saying ClassName.class_method() inside an instance method, you can use the constructor property instead: #constructor.class_method(). Also, you usually say #method() or #property rather than this.method() and this.property in CoffeeScript.