回调已被调用

Question

当我尝试在 node.js 的 async.waterfall 中使用 list.forEach 方法时，我收到了错误消息： if (fn === null) throw new Error("Callback is already called.");

错误：回调已被调用。

我想要的是对目录中的每个文件进行一些更改。

/**
 * Created by slow_time on 2017/3/22.
 */
var fs = require('fs');
var async = require('async');
var _dir = './data/';
//writeStream is used to log something
var writeStream = fs.createWriteStream('log.txt',
    {
        'flags': 'a',
        'encoding': 'utf8',
        'mode': 0666
    });

try {
    //use the method waterfall
    async.waterfall([
        //read the directory
        function (callback) {
            fs.readdir(_dir, function (err, files) {
                callback(err, files);
            });
        },
        function (files, callback) {
            //Here is what I guess, something wrong with it
            files.forEach(function (name) {
                callback(null, name);
            });
        },
        //The code below is right, I think.
        function (file, callback) {
            fs.stat(_dir + file, function (err, stats) {
                if(stats.isFile())
                    callback(err, stats, file);
            });
        },
        //judge whether it is a file or a directory
        function (stats, file, callback) {
            fs.readFile(_dir + file, 'utf8', function (err, data) {
                callback(err, file, data);
            });
        },
        // do some changes to the file content
        function (file, data, callback) {
            var adjData = data.replace(/somecompany\.com/g, 'burningbird.net');
            fs.writeFile(_dir + file, adjData, function (err) {
                callback(err, file);
            });
        },
        //write the changes back to the file
        function (file, callback) {
            writeStream.write('changed ' + file + '\n', 'utf8', function (err) {
                callback(err, file);
            });
        }
    ], function (err, result) {
        if(err) throw err;
        console.log('modified ' + result);
    });
} catch(err) {
    console.log(err);
}

Answer 1

当您在 foreach 中调用回调时，它会给出错误。 你的代码 -

files.forEach(function (name) {
   callback(null, name);
});

回调应该在您完成操作后只调用一次。 所以做这个改变：

files.forEach(function (name) {

});
callback(null, name);