I want to be able to write:
generate 'Cat', 'meow'
and define the generate function in such a way that it produces:
class Cat
meow: ->
#.__proto__.constructor.name + ' says meow.'
so that I can write:
garfield = new Cat
garfield.meow() # "Cat says meow"
If you don't mind polluting your global namespace, I actually got this snippet running in the 'try coffeescript' runner at the CoffeeScript site:
root = exports ? window
alert = alert or console.log
gen = (clsname, val) ->
root[clsname] = class
meow: => "#{clsname} says #{val}"
gen 'Cat', 'meow'
g = new root.Cat
alert g.meow()
gen 'Dog', 'woff'
d = new root.Dog
alert d.meow()
Not 100% what you asked for, but it's almost what you wanted, isn't it?
Edit: Actually, the first script only worked in the browser, not the (Node.js-based) CLI, corrected the script.
If you know you'll only live in the browser, you can loose root.Cat and only say Cat, but if you want Node.js and browser compat, you'll have to live with root.*
Edit 2: It's generally a better idea to return the class from the generating function rather than magically putting it in a namespace. It's also possible to make the method names dynamic. With some inspiration from #Loren, the asker (notice how it doesn't need to refer the global object anymore):
alert = alert or console.log
gen = (clsname, val) ->
C = class
C.prototype[val] = -> "#{clsname} says #{val}"
C
Cat = gen 'Cat', 'meow'
console.log Cat
g = new Cat
alert g.meow()
Dog = gen 'Dog', 'woff'
d = new Dog
alert d.woff()
If by "named class" you mean "a class with a named function," what you're asking for isn't possible—in CoffeeScript or JavaScript. Without eval, there's no way to create the equivalent of function FuncName() {...}. You can only use the __proto__.constructor.name property on functions defined with that syntax.
The class syntax is the only way of creating named functions in CoffeeScript, for reasons explained in the FAQ.
Related
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')
I have a class Child which extends Test. I want to call a function from Test from Child.
I tried this:
class Test
constructor: ->
#i = 'hello world'
f1: -> console.log #i
f2: -> console.log 'hello'
class Child extends Test
run: ->
Test::f1()
hello = new Child()
hello.run()
When I call hello.run(), it calls Test.f1(), but the result is undefined. It's not setting the static variable #i before it's running Test.f1().
If I switch Test::f1() to Test::f2(), it gives me the correct result.
I need to know how should I make Test's constructor run when I create a new Child() so that #i is defined in Test when I run Test::f1() from Child.run().
Thanks! :D
Here's one way of doing it:
class Test
#i: 'hello world'
#f1: -> console.log #i
f2: -> console.log 'hello'
class Child extends Test
run: ->
Test.f1()
hello = new Child()
hello.run()
Notice, the i variable is static, so it doesn't make sense to set it in the constructor. Also, the f1 method is now static as well.
(I'm not an expert with CoffeeScript, so I'm not sure what the :: syntax is needed for.)
The constructor is being run when you create a new instance of Child. The problem is the way that you're invoking f1.
You don't want to say Test::f1(). You can just say #f1(), since Child is a subclass of Test. These are different in a very important way: Test::f1() does not set this, so when that function requests this.i, it finds only undefined, because this is set to Window (or something ridiculous like that in the browser, not sure if you're running this in Node). Saying #f1() is the same as saying Test::f1.call(this). This is one of the nice things that CoffeeScript's class system lets you do.
Finally, a pedantic note: there are no static variables in the code you've written. i, as you've written it, is an instance variable. Static variables look like this:
class Test
#staticVar = 1234
Or like this:
class Test
# ...
Test.staticVar = 1234
Instance variables look like this:
class Test
fn: ->
#instanceVar = 1234
Or like this:
test = new Test()
test.instanceVar = 1234
Or even like this (for the default value of an instance variable shared among all instances):
Test::instanceVar = 1234
In a similar vein:
When I call hello.run(), it calls Test.f1(), but the result is undefined. It's not setting the static variable #i before it's running Test.f1().
You're never calling Test.f1(); you're calling Test::f1(), which is very different. In the code you've written, there is no Test.f1, only Test.prototype.f1.
Rails 3.2.8. In converting some of my JS functions over to CoffeeScript, I have come across several questions that say declaring a function like so:
#foo = (bar) ->
puts foo in the global namespace. But it doesn't, because my function calls elsewhere in the application, especially ones that are in .js.erb files.
Here's what does work:
foo = (bar) ->
window.foo = foo
With that, all my calls in .js.erb files work fine.
What is the reason that the #foo = notation doesn't work as I am expecting it to? That would be a lot easier than having to remember to add an extra line to expose the function to the global namespace.
#foo translates to this.foo
foo translates to var foo
There is a big difference between the two of those.
For example:
bar = (baz) ->
#bar = 5
lemon = #bar + baz
#foo = (bar) ->
lemon
return #
Bar = new bar(12)
Translates to:
var Bar, bar;
bar = function(baz) {
var lemon;
this.bar = 5;
lemon = this.bar + baz;
this.foo = function(bar) {
return lemon;
};
return this;
};
Bar = new bar(12);
See fiddle demo of generated code: http://jsfiddle.net/maniator/rXWw2/
Here is a link showing you the CoffeeScript and it's generated code
I just wanted to add something that seems important to understanding why the initial
#foo = () -> "abc"
doesn't add to the global window object.
Coffeescript wraps - once compiled, it wraps all contents of every .coffee-file into a surrounding anonymous function that is immediately executed.
Thusly, and explicitely for that reason, the global namespace is not polluted, thereby implicitely protecting the dev from creating "evil" globals.
So, your foo becomes a member function of an anonymous wrapper function - how seriously useless gg ...
I guess what you want anyway is your global config object or something, to which you simply add your definitions --- you surely didn't mean to really create globals just for quick and easy access now, did you?? :)
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.