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