这个错误函数的目的是什么 "next(err, err || doc._id)"

Question

我试图了解以下函数中发生的情况：

   next(err, err || doc._id) 

我对此进行了一些研究，但找不到任何解释 next 函数的文档。有人能解释一下它的用途吗？

function createQuestions(storyPrettyId, questions, author, callback) {
    async.map(
        questions,
        function(question, next) {
            QuestionMongoModel.create({
                storyPrettyId: storyPrettyId,
                title: question.title,
                answers: question.answers,
                author: author
            }, function(err, doc) {
                next(err, err || doc._id)
            })
        }, 
        callback
    )
}

Answer 1

答案在 async.map() 的文档中：

Arguments

• arr - An array to iterate over.
• iterator(item, callback) - A function to apply to each item in arr. The iterator is passed a callback(err, transformed) which must be called once it has completed with an error (which can be null) and a transformed item.
• callback(err, results) - Optional A callback which is called when all iterator functions have finished, or an error occurs. Results is an array of the transformed items from the arr.

next 只是您传递给 async.map() 的 iterator() 函数的 callback 参数。