Strange behavior with async module .map

Question

exports.fakeAccounts = function (Account, callback) {
  async.map([{
    username: 'Jehoon',
    provider: 'farcebook'
  }, {
    username: 'C3P0',
    provider: 'farcebook'
  }], function (opts, cb) {
    Account.upsert(opts, cb);
  }, callback);
};

Works fine, but

exports.fakeAccounts = function (Account, callback) {
  async.map([{
    username: 'Jehoon',
    provider: 'farcebook'
  }, {
    username: 'C3P0',
    provider: 'farcebook'
  }], Account.upsert, callback);
};

throws an error, saying that Account is undefined.

I would have thought that since Account.upsert takes the same arguments it would work. I've solved it for now, but I'm wondering what I'm missing here.

Community · Accepted Answer · 2017-05-23 10:26:11Z

1

This doesn't work because the Account.upsert method uses the this value and JavaScript has dynamic this.

You can try binding it explicitly to the this value:

exports.fakeAccounts = function (Account, callback) {
  async.map([{
    username: 'Jehoon',
    provider: 'farcebook'
  }, {
    username: 'C3P0',
    provider: 'farcebook'
  }], Account.upsert.bind(Account), callback);
};

edited May 23, 2017 at 10:26

CommunityBot

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answered Mar 1, 2014 at 1:20

Benjamin Gruenbaum

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3 Comments

Qantas 94 Heavy Over a year ago

This issue is also noted in "Common Pitfalls" on their GitHub readme: github.com/caolan/async/blob/master/README.md#common-pitfalls

Benjamin Gruenbaum Over a year ago

Oh cool, I didn't know that @Qantas94Heavy . I guess it's a common problem when using async if they have a whole section for it.

Jehan Over a year ago

Wow, thanks. Sorry for the dumb question. Hopefully it can save future developers from having to read the docs!

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