javascript - Q promises 在 lodash reduce 函数中不起作用

Question

我正在尝试返回具有最早修改日期的目录中的文件。这种方法似乎在 createFileDateMap 函数中失败了。我想减少一组文件路径并创建一个包含文件名和修改日期的对象。 getModDate 函数是一个异步的 fs.lstat 调用。我似乎无法将 reducer 的 acc 设置为 .then() block 中的值。当值取决于异步调用时，我不确定如何实现减少

var _ = require('lodash'),
    fs = require('fs'),
    path = require('path'),
    Q = require('q');

function checkDir(dir) {
    // Check if given path is valid directory
    var deferred = Q.defer();
    fs.lstat(dir, deferred.makeNodeResolver());
    return deferred.promise.invoke('isDirectory');
}

function getFiles(dir) {
    // Get all files within a directory
    var deferred = Q.defer();
    fs.readdir(dir, deferred.makeNodeResolver());
    return deferred.promise;
}

function makeFullPathFileArr(dir, files) {
    // Return array of full paths
    return _.map(files, function(file) {
        return path.join(dir, file);
    });
}

function getModDate(file) {
    // Return modification date of file
    var deferred = Q.defer();
    fs.stat(file, deferred.makeNodeResolver());
    return deferred.promise.get('mtime');
}

function createFileDateMap(filesArr) {
    // Return an obj of file paths and modification dates as Date objects
    // {{ file1: Date, file2: Date }}
    var fileDateMap = _.reduce(filesArr, function(acc, file) {
        getModDate(file)
            .then(function(modDate) {
                acc[file] = moment(modDate);
            });
        return acc;
    }, {});
    return fileDateMap;
}

function getMinDateFile(mapObj) {
    // return the file name which has the earliest modification date
    var dates = _.transform(mapObj, function(result, date, key) {
        result[key] = new Date(date);
    });
    var minDate = new Date(Math.min.apply(null, _.values(dates)));
    var invertedMapObj = _.invert(mapObj);

    return invertedMapObj[minDate];
}

var dir = '../reports';
checkDir(dir)
    .then(function(exist) {
        if(exist) {
            getFiles(dir)
                .then(function(fileNames) {
                    return makeFullPathFileArr(dir, fileNames);
                })
                .then(function(fullpathsArr) {
                    return createFileDateMap(fullpathsArr);
                })
                .then(function(fileAndDatesObj) {
                    console.log(getMinDateFile(fileAndDatesObj));
                });
        }
    })
    .catch(function(err) {
        console.log(err);
    });

Answer 1

感谢@BenjaminGruenbaum 的帮助。 :)

function createFileDateMap(filesArr) {
    // Return an obj of file paths and modification dates as Date objects
    // {{ file1: Date, file2: Date

    return Q.all(_.map(filesArr, getModDate))
        .then(function(modDates) {
           return _.zipObject(filesArr, modDates);
        });
}