匿名函数作为回调，但定义的函数不 [英] Anonymous function works as callback but defined function does not

问题描述

我有一个类似这样的模块：

  module.exports = AtomMarkdownLabels = 
 
 
 file_changed_added：（file_path）=> 
 fs.readFile file_path，'utf-8'，@process_yaml 
 console.log'file changed'
 
 process_yaml：（err，data）=> 
 console.logprocess_yaml被称为
  

我知道 file_changed_added 正在从一些其他函数调用，我看到控制台中的文件已更改输出，但 process_yaml 不是如果我更改 file_changed_added 到

  file_changed_added：（file_path）=> 
 fs.readFile file_path，'utf-8'，（err，data）=> 
 console.logtest
 console.log'file changed'
  

我看到正确调用测试和文件更改。可能发生什么？

解决方案

=> 有两个略有不同的用途：

1. 定义命名函数（ f = => ... ）或匿名函数 f（x，=> ...））， => c $ c> @ 与周围环境中的 @ 相同。




2. 在类中定义方法时：

     class C 
   m：=> ... 
     

   => @ <将是 C 的实例。 / p>




这两个用法都是创建一个绑定函数，但它们绑定到不同的东西。

您正在使用此结构：

  obj = 
 func：=& 
＃... 
  

这相当于：

  f = => 
＃... 
 obj = 
 func：f 
  

因为你使用一个普通的旧对象而不是一个类。那么 AtomMarkdownLabels 定义之外的是什么？ @ @ 不会是有用的，特别是它不会是你的 AtomMarkdownLabels 对象，有 process_yaml 属性，因此 @process_yaml 内部 file_changed_added 未定义或错误。

我不知道Atom希望你返回什么，应该工作，像这样：

 ＃使用类，以便=> gt;做你期望它做的事
 class AtomMarkdownLabels 
＃其他的东西在这里
 
 file_changed_added：（file_path）=> 
 fs.readFile file_path，'utf-8'，@process_yaml 
 console.log'file changed'
 
＃你可能需要或可能不需要=>这里
 process_yaml：（err，data）=> 
 console.logprocess_yaml被调用
 
＃导出类的实例
 module.exports = new AtomMarkdownLabels 
  

如果你想要或必须使用一个普通对象，那么你可以绕过 @ ：

 ＃只是简单的旧函数，所以这样定义
 process_yaml =（err，data） 
 console.logprocess_yaml被调用
 
 file_changed_added =（file_path） - > 
 fs.readFile file_path，'utf-8'，process_yaml 
 console.log'file changed'
 
 module.exports = AtomMarkdownLabels = 
 b 
 $ b file_changed_added：file_changed_added 
  

或这样：

 ＃明确命名你的对象，而不是使用@ 
 module.exports = AtomMarkdownLabels = 
＃其他的东西在这里
 
 file_changed_added：（file_path） - > 
 fs.readFile file_path，'utf-8'，AtomMarkdownLabels.process_yaml 
 console.log'file changed'
 
 process_yaml：（err，data） - > 
 console.logprocess_yaml被称为
  

---

这应该可以解决几天前您的其他 CoffeeScript问题。

I have a module that looks like this:

module.exports = AtomMarkdownLabels =
  # other stuff here

  file_changed_added: (file_path) =>
    fs.readFile file_path, 'utf-8', @process_yaml
    console.log 'file changed'

  process_yaml: (err, data) =>
    console.log "process_yaml is called"

I know file_changed_added is being called from some other function and I'm seeing the "file changed" output in the console, but process_yaml isn't if I change file_changed_added to

file_changed_added: (file_path) =>
    fs.readFile file_path, 'utf-8', (err, data) =>
      console.log "test"
    console.log 'file changed'

I see both "test" and "file changed" being called properly. What could be going on?

解决方案

=> has two slightly different purposes:

1. When defining a named function (f = => ...) or anonymous function f(x, => ...)), => simply ensures that @ inside the function is that same as @ in the surrounding context.

2. When defining a method in a class:

   class C
     m: => ...
   

   => ensures that @ inside m will be the instance of C.

Both uses are creating a bound function but they're binding to different things.

You're using this structure:

obj =
  func: =>
    # ...

That's equivalent to this:

f = =>
  # ...
obj =
  func: f

because you're using a plain old object rather than a class. So what is @ outside your AtomMarkdownLabels definition? @ won't be anything useful and in particular, it won't be your AtomMarkdownLabels object and it won't have a process_yaml property so @process_yaml inside file_changed_added is going to be undefined or an error.

I'm not sure what specifically Atom wants you to return but a class should work, something like this:

# Use a class so that => does what you're expecting it to do
class AtomMarkdownLabels
  # other stuff here

  file_changed_added: (file_path) =>
    fs.readFile file_path, 'utf-8', @process_yaml
    console.log 'file changed'

  # you may or may not need => here
  process_yaml: (err, data) =>
    console.log "process_yaml is called"

# Export an instance of your class
module.exports = new AtomMarkdownLabels

If you want to or must use a plain object then you could bypass @ completely and do it like this:

# Just plain old functions so define them that way
process_yaml = (err, data) ->
  console.log "process_yaml is called"

file_changed_added = (file_path) ->
  fs.readFile file_path, 'utf-8', process_yaml
  console.log 'file changed'

module.exports = AtomMarkdownLabels =
  # other stuff here

  file_changed_added: file_changed_added

or like this:

# Explicitly name your object rather than using @
module.exports = AtomMarkdownLabels =
  # other stuff here

  file_changed_added: (file_path) ->
    fs.readFile file_path, 'utf-8', AtomMarkdownLabels.process_yaml
    console.log 'file changed'

  process_yaml: (err, data) ->
    console.log "process_yaml is called"

---

This should solve your other CoffeeScript problem from a few days ago too.

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