带有回调函数的 Coffeescript简化的错误处理

Question

我希望能够将这个 CoffeeScript 代码的错误处理重构

# Do some stuff with 2 levels of asynchronous callbacks and error handling
vote = (res, data) ->
  Case.findOne { caseId: data.id }, (err, mycase) ->
    if err
      console.error 'Vote failed'
    else
      myvote = new Vote
        case: mycase._id
      myvote.save (err) ->
        if err
          console.error 'Could not add vote'
        else
          console.log 'Success!'

为这样的内容：

# Run my function, do error handling, and run the callback if no error
runit = (func, arg, errmsg, callback) ->
  func arg, (err, docs) ->
    if err
      console.log errmsg + ': ' + err
    else
      callback docs

# Original code, simplified
vote = (res, data) ->
  runit Case.findOne { caseId: data.id }, 'Vote failed', (mycase) ->        
      myvote = new Vote
        case: mycase._id
      runit myvote.save, 'Could not add vote', () ->   
          console.log 'Success!'

显然，runit 函数需要能够正确处理一个或多个参数，但我没有尝试这样做正确编码。

如果我像这样运行它，我会得到一个错误：

node.js:201
    throw e; // process.nextTick error, or 'error' event on first tick
          ^
TypeError: Cannot read property 'findOne' of undefined
    at /tmp/node_modules/mongoose/node_modules/hooks/hooks.js:27:28
    at /tmp/lib/api.js:227:12
    at Promise.<anonymous> (/tmp/lib/api.js:216:16)
    at Promise.<anonymous> (/tmp/node_modules/mongoose/lib/promise.js:120:8)
    at Promise.<anonymous> (events.js:67:17)
    at Promise.emit (/tmp/node_modules/mongoose/lib/promise.js:59:38)
    at Promise.complete (/tmp/node_modules/mongoose/lib/promise.js:70:20)
    at /tmp/node_modules/mongoose/lib/query.js:885:15
    at model.<anonymous> (/tmp/node_modules/mongoose/lib/document.js:181:5)
    at model.init (/tmp/node_modules/mongoose/lib/model.js:181:36)

Answer 1

# Run my function, do error handling, and run the callback if no error
runit = (func, args..., errmsg, callback) ->
  func args..., (err, docs) ->
    if err
      return console.log errmsg + ': ' + err
    callback docs

# Original code, simplified
vote = (res, data) ->
  runit Case.findOne { caseId: data.id }, 'Vote failed', (mycase) ->        
    myvote = new Vote
      case: mycase._id
    runit myvote.save, 'Could not add vote', ->   
      console.log 'Success!'

runit 编译为：

runit = function() {
  var args, callback, errmsg, func, _i;
  func = arguments[0], args = 4 <= arguments.length ? __slice.call(arguments, 1, _i = arguments.length - 2) : (_i = 1, []), errmsg = arguments[_i++], callback = arguments[_i++];
  return func.apply(null, __slice.call(args).concat([function(err, docs) {
    if (err) return console.log(errmsg + ': ' + err);
    return callback(docs);
  }]));
};

Answer 2

使用提前返回而不是条件分支，这样可以使代码保持简单和理智，并避免不必要的样板代码。

vote = (res, data) ->
  Case.findOne { caseId: data.id }, (err, mycase) ->
    return console.error 'Vote failed' if err?
    myvote = new Vote
      case: mycase._id
    myvote.save (err) ->
      return console.error 'Could not add vote' if err?
      console.log 'Success!'

Answer 3

我是Caolan 的异步库的忠实粉丝。该库的主要思想是每个回调的第一个参数都是错误，如果不存在错误，则调用链中的下一个函数。所以你的可能看起来像这样：

vote = (res, data) ->
  async.series [
    (next) -> Case.findOne { caseId: data.id }, next
    (next) -> myvote = new Vote({case: mycase_id}).save(next)
  ], (err, result) ->
    if err
      console.error err
    else
      console.log "Success!"

函数链在抛出第一个错误时中断，这样你的最终回调实际上只负责处理单个错误。这对于您想要停止并报告遇到的第一个问题的串行流程非常有用。