节点async.js：回调不是函数错误？

Question

我有这个代码：

async = require('async')

async.auto({
   getUserName: function(callback) {
      console.log('**In getUserName.**')
      callback(null, 'Lem')
   },

   connectToDb: function(callback) {
      console.log('**In connectToDb.**')
      var connected = true
      if(connected) {
        callback(null, connected)
      } else {
        callback('Error connecting to DB.', null)
      }
   },

   checkIfUserExist: [
      'getUserName',
      'connectToDb',
      function(callback, results) {
         console.log('**In checkIfUserExist.**',          
            JSON.stringify(results))
         var userExist = false
         if(userExist) {
            callback('User exist in DB.')
         } else {
            setTimeout(
               function() {
                  callback(null, userExist);
               },
               1000
            );
         }
      }
   ],

   signup: [
      'checkIfUserExist',
      function(callback, results) {
         console.log('**In signup**', JSON.stringify(results))
         var userName = results.getUserName
         var isDbConnected = results.connectToDb
         var userExist = result.checkIfUserExist

        if(userName && isDbConnected && !userExist) {
           callback(null, 
             {'status': '200', 'msg': 'Successfully signed up user'})
       } else {
          callback('Error signing up user.', null)
       }
    }
  ]
 },
 function(error, results) {
    console.log('error = ', error)
    console.log('results = ', results)

})

为什么我遇到这个错误：

**In getUserName.**
**In connectToDb.**
error =  function () {
    if (fn === null) throw new Error("Callback was already called.");
        var callFn = fn;
        fn = null;
    callFn.apply(this, arguments);
}
results =  undefined
**In checkIfUserExist.** undefined
^[[A/home/lem/js/async/asyncAuto.js:30
        callback(null, userExist);
        ^

TypeError: callback is not a function
   at Timeout._onTimeout (/home/lem/js/async/asyncAuto.js:30:13)
   at ontimeout (timers.js:365:14)
   at tryOnTimeout (timers.js:237:5)
   at Timer.listOnTimeout (timers.js:207:5)

Answer 1

一个异步函数，一个期望回调作为其最后一个参数的函数。这是我的工作代码。

    var async = require('async');
         async.auto({
           getUserName: function(callback) {
            console.log('**In getUserName.**')
            callback(null, 'Lem')
           },

         connectToDb: function(callback) {
          console.log('**In connectToDb.**')
          var connected = true
          if(connected) {
            callback(null, connected)
          } else {
            callback('Error connecting to DB.', null)
          }
       },
       checkIfUserExist: [
          'getUserName',
          'connectToDb',
          function(results, callback) {
             console.log('**In checkIfUserExist.**',          
                JSON.stringify(results))
             var userExist = false
             if(userExist) {
                callback('User exist in DB.')
             } else {               
                setTimeout(function() {                 
                      callback(null, userExist);
               },1000);
             }
          }
       ],

       signup: [
          'checkIfUserExist',
          function(results, callback) {
             console.log('**In signup**', JSON.stringify(results))
             var userName = results.getUserName
             var isDbConnected = results.connectToDb
             var userExist = results.checkIfUserExist

            if(userName && isDbConnected && !userExist) {
               callback(null, 
                 {'status': '200', 'msg': 'Successfully signed up user'})
           } else {
              callback('Error signing up user.', null)
           }
        }
     ],
},
     function(error, results) {
        console.log('error = ', error)
        console.log('results = ', results)         
    })

function(callback, results) 应该是 function(results, callback)

请检查此 url 以供参考。 https://caolan.github.io/async/docs.html#auto

Answer 2

v2 中异步的 auto 方法发生了重大变化，您似乎正在使用它。 https://github.com/caolan/async/blob/master/CHANGELOG.md#breaking-changes

auto task functions now always take the callback as the last argument. If a task has dependencies, the results object will be passed as the first argument. To migrate old task functions, wrap them with _.flip

节点async.js：回调不是函数错误？

Node async.js: callback is not a function error?

node.js

async.js