Using CoffeeScript to Invoke Methods

Question

Using CoffeeScript to Invoke Methods

I'm still learning CoffeeScript and encountering some challenges with calling methods. Can someone help me out?

Here is the Card model I am working with:

class exports.Card extends Backbone.Model
  defaults:
    pip:   '4'
    suit:  '♠'
    color: 'b'

  rows: ->
    rows =
      '4': [2, 0, 2]
    rows[@pip]

Looking at a snippet from the template:

<ul class="col cols-<%= @card.rows()[0] %>">

When running this code, I'm getting an error message saying

Uncaught TypeError: Object #<Object> has no method 'rows'

I am uncertain if I am using the correct syntax for the rows method in the Card model, or if there is something else I am missing. Any insights would be appreciated. Thank you!

Update:

I've noticed that @card.property always works, but @card.any_method() does not. Currently, I am working around this by using properties, but I would like to understand why this behavior is happening. Thanks for your assistance!

Update 2:

In case it helps, I am using . Here's a snippet from the main.coffee file showing how the @card instance is created and passed to the view.

window.app = {}
app.routers = {}
app.models = {}
app.collections = {}
app.views = {}

Card = require('models/card_model').Card
MainRouter = require('routers/main_router').MainRouter
HomeView = require('views/home_view').HomeView
CardView = require('views/card_view').CardView

# app bootstrapping on document ready
$(document).ready ->
  app.initialize = ->
    app.routers.main = new MainRouter()
    app.views.home = new HomeView()
    app.views.card = new CardView(model: new Card(color: 'r', suit: '♥', pip: '7'))
    app.routers.main.navigate 'home', true if Backbone.history.getFragment() is ''
  app.initialize()
  Backbone.history.start()

javascript syntax backbone.js coffeescript

Answer 1

Answer №1

Your way of calling methods is on point. CoffeeScript adheres to the following rules:

Using parentheses for method calls with arguments is optional, like this:
```
object.method 1,2 
```
or
```
object.method(1,2)
```
However, using parentheses for method calls without arguments is mandatory, like this:
```
object.method()
```

To understand how this works, test the following code on the 'Try CoffeeScript' editor on the CoffeeScript website:

class A
  method: ->
    console.log "A"

(new A()).method();

Given that your method call syntax is correct, it is probable that the issue lies in the @card variable not being an instance of the exports.Card class.

Answer 2

Your way of calling methods is on point. CoffeeScript adheres to the following rules:

Using parentheses for method calls with arguments is optional, like this:
```
object.method 1,2 
```
or
```
object.method(1,2)
```
However, using parentheses for method calls without arguments is mandatory, like this:
```
object.method()
```

To understand how this works, test the following code on the 'Try CoffeeScript' editor on the CoffeeScript website:

class A
  method: ->
    console.log "A"

(new A()).method();

Given that your method call syntax is correct, it is probable that the issue lies in the @card variable not being an instance of the exports.Card class.

Answer 3

Answer №2

The issue arises from the fact that pip is not a property of the Card instance; rather, it belongs to Card::defaults, causing Backbone to treat it as an attribute of the Card instance instead of a property. To access the pip attribute, you can use the following:

card.get 'pip'

or directly access it as:

card.attributes.pip

The reason behind this differentiation lies in the fact that, in JavaScript, monitoring a property for changes is not feasible, a functionality that Backbone requires to dispatch events. For example, modifying pip with card.set 'pip' triggers a "change" event in Backbone.

To resolve the issue, simply update the last line of the rows method as follows:

rows: ->
  rows =
    '4': [2, 0, 2]
  rows[@get 'pip']

(Note: While some JavaScript environments support getters/setters, enabling you to use card.pip = ... instead of card.set 'pip', ..., Backbone opts out of this approach to maintain compatibility with all modern-ish browsers. For more information on this topic, refer to John Resig's article available here.)

Answer 4

The issue arises from the fact that pip is not a property of the Card instance; rather, it belongs to Card::defaults, causing Backbone to treat it as an attribute of the Card instance instead of a property. To access the pip attribute, you can use the following:

card.get 'pip'

or directly access it as:

card.attributes.pip

The reason behind this differentiation lies in the fact that, in JavaScript, monitoring a property for changes is not feasible, a functionality that Backbone requires to dispatch events. For example, modifying pip with card.set 'pip' triggers a "change" event in Backbone.

To resolve the issue, simply update the last line of the rows method as follows:

rows: ->
  rows =
    '4': [2, 0, 2]
  rows[@get 'pip']

(Note: While some JavaScript environments support getters/setters, enabling you to use card.pip = ... instead of card.set 'pip', ..., Backbone opts out of this approach to maintain compatibility with all modern-ish browsers. For more information on this topic, refer to John Resig's article available here.)

Answer 5

Answer №3

After a light bulb moment, I realized my error - I had overlooked the fact that the @card variable mentioned in the template was not coming from the main.coffee file. Instead, it was being transformed into JSON in the CardView class as shown below:

cardTemplate = require('templates/card')

class exports.CardView extends Backbone.View
  tagName: 'div'
  className: 'card'

  render: ->
    $(@el).html cardTemplate(card: @model.toJSON())
    @

It finally clicked why only variables were functioning correctly, and methods were not - the @card was essentially a JSON representation of the model instance.

Thank you all for the helpful suggestions and clarifications - my apologies for the silly oversight :P

Answer 6

After a light bulb moment, I realized my error - I had overlooked the fact that the @card variable mentioned in the template was not coming from the main.coffee file. Instead, it was being transformed into JSON in the CardView class as shown below:

cardTemplate = require('templates/card')

class exports.CardView extends Backbone.View
  tagName: 'div'
  className: 'card'

  render: ->
    $(@el).html cardTemplate(card: @model.toJSON())
    @

It finally clicked why only variables were functioning correctly, and methods were not - the @card was essentially a JSON representation of the model instance.

Thank you all for the helpful suggestions and clarifications - my apologies for the silly oversight :P

Using CoffeeScript to Invoke Methods

Answer №1

Answer №2

Answer №3

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