javascript - 另一个 CoffeeScript 错误

Question

嘿，我刚刚在学习 CoffeeScript，但我总是遇到错误。这是我的代码:

Db   = require('./lib/mongodb').Db
ObjectID = require('./lib/mongodb').ObjectID
Server   = require('./lib/mongodb').Server

class UserDataProvider
    constructor = (host,port)->
        this.db = new Db( 'test' , new Server(host ,port,{}))
    getCollection = (callback) ->
        this.db.collection 'data',(error,data)->
            if error then callback(error)
            else callback(data)
    findAll = (callback) ->
        this.getCollection (error,data)->
            if error then callback error
            else
                data.find (error, cursor) ->
                    if error then callback error
                    else
                        cursor.toArray (error, results)->
                            if error then callback error
                            else callback(null,results)
    findById = (id,callback)->
        this.getCollection (error, data)->
          if error then callback error
          else
            data.findOne { _id: id} , (error, result)->
              if error then callback error
              else callback(null, result)
    save = (data, callback)->
        this.getCollection (error, collection)->
            if error then callback error
            else
                if typeof(data.length) is "undefined"
                then data = [data]

                collection.insert data ()->
                    callback null, data

exports.UserDataProvider = UserDataProvider

当我尝试使用 userdataprovider.save( ?? BLAH BLAH BLAH ??)//我已经实例化了它。

我收到这个错误:

TypeError: Object #<UserDataProvider> has no method 'save'
    at Object.<anonymous> (/home/akshay/dev/statServer/app.js:8:15)
    at param (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:146:21)
    at param (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:157:15)
    at pass (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:162:10)
    at Object.router [as handle] (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:168:6)
    at next (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/index.js:218:15)
    at Object.handle (/usr/local/lib/node/.npm/express/1.0.7/package/lib/express/server.js:65:5)
    at next (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/index.js:218:15)
    at Server.handle (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/index.js:231:3)
    at Server.emit (events.js:45:17)

如果重要的话，我正在使用 Expressjs 和 Nodejs 以及原生 MongoDB 驱动程序

Answer 1

问题是您使用 = 而不是 : 来定义实例级方法。

CoffeeScript 的 class 构造是对象和函数的奇怪混合体。类体内的代码立即运行——例如，

class UserDataProvider
    a = 'foo'
    console.log a

打印foo。但是，当您使用对象语法 key: value 时，您定义了原型(prototype)的属性(特殊关键字 constructor 除外):

class UserDataProvider
  a: 'foo'

(new UserDataProvider).a   # 'foo'

这可能看起来很奇怪，但它允许您运行非常有用的一次性静态初始化代码，包括只能由类中定义的方法看到的私有(private)变量:

class UserDataProvider
    secretPassword = Math.random()
    getHash: -> hash(secretPassword)

长话短说:在定义实例属性时使用: 而不是=。 (对于静态属性，@a = b 和 @a: b 是等价的；都将 UserDataProvider.a 设置为 b.)