Backbone .on事件侦听器，带有带有coffeescript的回调函数

Question

How can I correctly write this in coffee script?

this.model.on('change:game', function(){
  this.render();
}, this)

I am trying everything I can think of, and I'm currently on this:

@model.on 'change:game', -> 
  @render()
@

I am confused how to handle multiple arguments when one of them is an anonymous function, the first 2 parameters have a comma, but if I try to add a comma before the 3rd parameter I get syntax errors.

Answer 1

I believe you can do something like this:

@model.on "change:game", => @render()

With CoffeeScript, you can leverage the "fat" arrows to lexically bind this and simplify your code.

Answer 2

You don't actually need an anonymous function. When you say:

model.on(event, fn, context)

in JavaScript, the event handling system will end up saying:

fn.apply(context, whatever_arguments_are_used)

The fn can by any function at all, it doesn't have to be anonymous.

Moving to CoffeeScript and remembering that @render is a reference to the render function, we can say:

@model.on 'change:game', @render, @

and skip the anonymous function altogether. Alternatively, you could use listenTo to automatically supply the desired @ :

@listenTo @model, 'change:game', @render

This sort of structure can be a problem if the fn above takes arguments that don't match what the event system will pass. In those cases, you can use a bound anonymous function as wmock suggests , the multiline approach you found, or some parentheses:

@model.on 'change:game', (-> @render()), @
#                        ^            ^ 

or listenTo again:

@listenTo @model, 'change:game', -> @render()

Answer 3

You have four ways:

1. simple

    @model.on 'change:game', -> @render() , @ 

2. fat arrow

    @model.on 'change:game', => @render() 

3. without anonymous function

    @model.on 'change:game', @render, @ 

4. with parenthesis

    @model.on 'change:game', (-> @render()), @ 

---

And Your second question about how to handle multiple parameters, when some of them are anonymous function.

Four examples, that explain everything:

param, func

func param1, () ->
  # anonymous function 1
  return

param, func, param

func param1, () ->
  # anonymous function 1
  return
, param2

param, func, func

func param1, () ->
  # anonymous function 1
  return
, () ->
  # anonymous function 2
  return

param, func, param, func

func param1, () ->
  # anonymous function 1
  return
, param2, () ->
  # anonymous function 2
  return