您可以通过多种不同的方式异步处理此代码。您可以使用节点async 库来更优雅地处理所有回调。如果您不想深入承诺，那么这就是“简单”的选择。我在引号中加上了easy，因为如果你足够了解promise，它们实际上会更容易。异步库很有帮助，但在错误传播方面仍有很多不足之处，并且您必须将所有调用都包含在其中的大量样板代码。
更好的方法是使用 Promise。 Async/Await 仍然很新。如果没有像 Bable 或 Typescript 这样的预处理器，甚至不支持节点 7（不确定节点 8）。此外，async/await 无论如何都会在底层使用 Promise。
这是我使用 Promise 的方法，甚至包括文件统计缓存以实现最佳性能：
const fs = require('fs');
const crypto = require('crypto');
const Promise = require('bluebird');
const fileList = ['file1', 'file2', 'file3'];
// Use Bluebird's Promise.promisifyAll utility to turn all of fs'
// async functions into promise returning versions of them.
// The new promise-enabled methods will have the same name but with
// a suffix of "Async". Ex: fs.stat will be fs.statAsync.
Promise.promisifyAll(fs);
// Create a cache to store the file if we're planning to get multiple
// stats from it.
let cache = {
fileName: null,
fileStats: null
};
const getFileStats = (fileName, prop) => {
if (cache.fileName === fileName) {
return cache.fileStats[prop];
}
// Return a promise that eventually resolves to the data we're after
// but also stores fileStats in our cache for future calls.
return fs.statAsync(fileName).then(fileStats => {
cache.fileName = fileName;
cache.fileStats = fileStats;
return fileStats[prop];
})
};
const getMd5Hash = file => {
// Return a promise that eventually resolves to the hash we're after.
return fs.readFileAsync(file).then(fileData => {
const hash = crypto.createHash('md5');
hash.update(fileData);
return hash.digest('hex');
});
};
// Create a promise that immediately resolves with our fileList array.
// Use Bluebird's Promise.map utility. Works very similar to Array.map
// except it expects all array entries to be promises that will
// eventually be resolved to the data we want.
let results = Promise.resolve(fileList).map(fileName => {
return Promise.all([
// This first gets a promise that starts resolving file stats
// asynchronously. When the promise resolves it will store file
// stats in a cache and then return the stats value we're after.
// Note that the final return is not a promise, but returning raw
// values from promise handlers implicitly does
// Promise.resolve(rawValue)
getFileStats(fileName, 'ctime'),
// This one will not return a promise. It will see cached file
// stats for our file and return the stats value from the cache
// instead. Since it's being returned into a Promise.all, it will
// be implicitly wrapped in Promise.resolve(rawValue) to fit the
// promise paradigm.
getFileStats(fileName, 'size'),
// First returns a promise that begins resolving the file data for
// our file. A promise handler in the function will then perform
// the operations we need to do on the file data in order to get
// the hash. The raw hash value is returned in the end and
// implicitly wrapped in Promise.resolve as well.
getMd5(file)
])
// .spread is a bluebird shortcut that replaces .then. If the value
// being resolved is an array (which it is because Promise.all will
// resolve an array containing the results in the same order as we
// listed the calls in the input array) then .spread will spread the
// values in that array out and pass them in as individual function
// parameters.
.spread((dateTime, fileSize, md5Hash) => [file, { dateTime, fileSize, md5Hash }]);
}).catch(error => {
// Any errors returned by any of the Async functions in this promise
// chain will be propagated here.
console.log(error);
});
这是代码，但没有 cmets 以便于查看：
const fs = require('fs');
const crypto = require('crypto');
const Promise = require('bluebird');
const fileList = ['file1', 'file2', 'file3'];
Promise.promisifyAll(fs);
let cache = {
fileName: null,
fileStats: null
};
const getFileStats = (fileName, prop) => {
if (cache.fileName === fileName) {
return cache.fileStats[prop];
}
return fs.statAsync(fileName).then(fileStats => {
cache.fileName = fileName;
cache.fileStats = fileStats;
return fileStats[prop];
})
};
const getMd5Hash = file => {
return fs.readFileAsync(file).then(fileData => {
const hash = crypto.createHash('md5');
hash.update(fileData);
return hash.digest('hex');
});
};
let results = Promise.resolve(fileList).map(fileName => {
return Promise.all([
getFileStats(fileName, 'ctime'),
getFileStats(fileName, 'size'),
getMd5(file)
]).spread((dateTime, fileSize, md5Hash) => [file, { dateTime, fileSize, md5Hash }]);
}).catch(console.log);
最终的结果将是一个类似的数组，它有望与您的原始代码的结果相匹配，但在基准测试中应该表现得更好：
[
['file1', { dateTime: 'data here', fileSize: 'data here', md5Hash: 'data here' }],
['file2', { dateTime: 'data here', fileSize: 'data here', md5Hash: 'data here' }],
['file3', { dateTime: 'data here', fileSize: 'data here', md5Hash: 'data here' }]
]
如有任何错别字，请提前致歉。没有时间或能力实际运行任何这些。不过我仔细看了一遍。
在发现 async/await 从 7.6 开始就在节点中后，我决定昨晚玩一下它。对于不需要并行完成的递归异步任务，或者您可能希望可以同步编写的嵌套异步任务，它似乎最有用。对于您在这里需要的东西，我可以看到没有任何令人兴奋的使用 async/await 的方法，但是有一些地方的代码可以更清晰地阅读。这是代码，但有一些小的异步/等待便利。
const fs = require('fs');
const crypto = require('crypto');
const Promise = require('bluebird');
const fileList = ['file1', 'file2', 'file3'];
Promise.promisifyAll(fs);
let cache = {
fileName: null,
fileStats: null
};
async function getFileStats (fileName, prop) {
if (cache.fileName === fileName) {
return cache.fileStats[prop];
}
let fileStats = await fs.stat(fileName);
cache.fileName = fileName;
cache.fileStats = fileStats;
return fileStats[prop];
};
async function getMd5Hash (file) {
let fileData = await fs.readFileAsync(file);
const hash = crypto.createHash('md5');
hash.update(fileData);
return hash.digest('hex');
};
let results = Promise.resolve(fileList).map(fileName => {
return Promise.all([
getFileStats(fileName, 'ctime'),
getFileStats(fileName, 'size'),
getMd5(file)
]).spread((dateTime, fileSize, md5Hash) => [file, { dateTime, fileSize, md5Hash }]);
}).catch(console.log);