javascript - async.waterfall 重复调用

Question

这个问题已经有答案了:

For-loop and async callback in node.js? (3 个回答)

已关闭 9 年前。

我有以下异步代码。

  for fileName in sourceFiles
    console.log 'dealing with ', fileName
    async.waterfall [
      (callback) ->
        console.log "going to read ", fileName
        fs.readFile fileName, (err, content) ->
          if err then throw err
          callback null, fileName, content
          return
      (fileName, content, callback) ->
        console.log 'length of: ',  fileName, ' is: ', content.length

我预计输出会是这样的:

dealing with file1
going to read file1
length of file1 is 10
dealing with file2
going to read file2
length of file 2 is 20

相反，我得到的是这样的:

dealing with file1
dealing with file2
going to read file2
going to read file2 <- note it is the same file repeated
length of file2 is 20
length of file2 is 20

我无法弄清楚为什么会这样。 (这是一个 CoffeeScript 没有问题。在 JS 中也有相同的输出)

Answer 1

async 库不会重复调用，但您在此处遇到范围界定问题。

当调用第一个函数时，循环中的 fileName 已设置为 file2，您应该尝试将其包装到另一个函数中，只是为了获得新的作用域工作，像这样:

for fileName in sourceFiles
  (fileName) ->
    console.log 'dealing with ', fileName
    async.waterfall [
      (callback) ->
        console.log "going to read ", fileName
        fs.readFile fileName, (err, content) ->
          if err then throw err
          callback null, fileName, content
          return
      (fileName, content, callback) ->
        console.log 'length of: ',  fileName, ' is: ', content.length