如何在coffeescript中将参数传递给匿名函数？

Question

Basically I need to pass an argument to an anonymous function in coffeescript, and I've ran out of ideas.

This is my code:

audio = {
        sounds: {},
        sources: [{
            wind: 'sounds/wind.mp3'
        }],
        load: (callback) ->
            this.totalFiles = Object.size(this.sources[0])
            for key of this.sources[0]
                sound = new Howl({ src: [this.sources[0][key]] })
                self = this
                sound.once('load', (key) =>
                    (key) ->
                        self.sounds[key] = this
                        if Object.size(self.sounds) == self.totalFiles
                            if typeof callback == 'function' then callback()
                (key)) <- THIS ARGUMENT PASSING DOES NOT COMPILE CORRECTLY
        loop: (name) ->
            this.sounds[name].loop(true)
            console.log this.sounds
    }

The code with callback.call():

load: (callback) ->
    this.totalFiles = Object.size(this.sources[0])
    for key of this.sources[0]
        sound = new Howl({ src: [this.sources[0][key]] })
        self = this
        sound.once('load', (key) =>
            callback.call(() ->
                self.sounds[key] = this
                if Object.size(self.sounds) == self.totalFiles
                    if typeof callback == 'function' then callback()
            , key)
        )

With callback.call() or callback.apply() I get the same result, the same compiled javascript. I tried to add (key) where I needed it in already compiled javascript, and it worked as intended.

Object size:

Object.size = (obj) ->
        size = 0
        for key in obj then if obj.hasOwnProperty(key) then size++
        return size

A good helper function I found on stackoverflow.

Answer 1

Your code has some issues that are likely hiding the real problem:

• Inconsistent indenting
• self = this the callback to sound.once is a fat arrow function, meaning that the line self.sounds[key] = this this and self are the same
• Inclusion of lots of unnecessary braces.
• Inconsistent use of commas in object property definitions.

AFAIK the actual problem is that you're trying to call an IIFE, and you need parens:

sound.once('load', ((key) =>
    (key) ->
         self.sounds[key] = this
         if Object.size(self.sounds) == self.totalFiles
            if typeof callback == 'function' then callback()
)(key))

Except that you've over-used the name key . You've got a function that you're partially applying with a parameter named key, and then the returned function also takes a parameter named key? Which is it?

Answer 2

This did the trick for me:

sound.once('load', ((key) =>
    () ->
        self.sounds[key] = this
            if Object.size(self.sounds) == self.totalFiles
                if typeof callback == 'function' then callback()
        )(key)
    )