使用异步模块触发一个回调，一旦所有文件都读 [英] Using async module to fire a callback once all files are read

问题描述

我使用 caolan的异步模块打开文件名的数组（在这种情况下，模板文件名）。

I'm using caolan's 'async' module to open an array of filenames (in this case, template file names).

每文档，我使用 async.forEach（），这样我就可以开火回调一旦所有操作完成。

Per the documentation, I'm using async.forEach(),so I can fire a callback once all operations have completed.

一个简单的测试案例是：

A simple test case is:

var async = require('async')
var fs = require('fs')

file_names = ['one','two','three'] // all these files actually exist

async.forEach(file_names, 
    function(file_name) {
        console.log(file_name)
        fs.readFile(file_name, function(error, data) {
            if ( error) {   
                console.log('oh no file missing')   
                return error
            } else {
                console.log('woo '+file_name+' found')
            }       
        })
    }, function(error) {
        if ( error) {   
            console.log('oh no errors!')
        } else {
            console.log('YAAAAAAY')
        }
    }
)

的输出如下所示：

The output is as follows:

one
two
three
woo one found
woo two found
woo three found

即，似乎最终的回调不点火。什么我需要做的，使最终的回调火？

I.e, it seems the final callback isn't firing. What do I need to do to make the final callback fire?

推荐答案

这是正在的所有项目运行必须采取一个回调，其结果传递给回调函数。见下面（我也分开read_a_file以提高可读性）：

The function that is being run across all items must take a callback, and pass its results to the callback. See below (I've also separated read_a_file to improve readability):

var async = require('async')
var fs = require('fs')

file_names = ['one','two','three']


    // This callback was missing in the question.
var read_a_file = function(file_name, callback) {
    console.log(file_name)
    fs.readFile(file_name, function(error, data) {
        if ( error) {   
            console.log('oh no file missing')   
            return callback(error)
        } else {
            console.log('woo '+file_name+' found')
            return callback()
        }       
    })
}

async.forEach(file_names, read_a_file, function(error) {
    if ( error) {   
        console.log('oh no errors!')
    } else {
        console.log('YAAAAAAY')
    }
})

返回：

one
two
three
woo one found
woo two found
woo three found
YAAAAAAY

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