chaining `fs.readdir` with a `.then` to return an array

问题

I am trying to create an array of specific files in a directory; which will go through a few test cases to make sure it fits a given criteria.

I'm using the fs.readdir method, but it doesn't return a promise meaning I cannot push to an array.

My idea was to populate an array (arr) with the files I actually want to output and then do something with that array. But because readdir is asynchronous and I can't chain a .then() onto it, my plans are quashed.

I've also tried the same thing with readdirSync to no avail.

const Promise = require('bluebird');
const fs = Promise.promisifyAll(require('fs'));

var arr = [];

fs.readdirAsync(folder).then( files => {
  files.forEach(file => {
    fs.stat(folder + '/' + file, (err, stats) => {
       if(!stats.isDirectory()) {
         arr.push(file);
        return;
      }
     });
   });
})
.then( () => {
  console.log(arr);
});

回答1:

fs.readdir is callback based, so you can either promisify it using bluebird (or writing a simple implementation of it yourself), or simply wrap the call in a promise, like so:

// Wrapped in a promise
new Promise((resolve, reject) => {
    return fs.readdir('/folderpath', (err, filenames) => err !== undefined ? reject(err) : resolve(filenames))
})

Or the custom promisify function:

// Custom promisify
function promisify(fn) {
  /**
   * @param {...Any} params The params to pass into *fn*
   * @return {Promise<Any|Any[]>}
   */
  return function promisified(...params) {
    return new Promise((resolve, reject) => fn(...params.concat([(err, ...args) => err ? reject(err) : resolve( args.length < 2 ? args[0] : args )])))
  }
}

const readdirAsync = promisify(fs.readdir)
readdirAsync('./folderpath').then(filenames => console.log(filenames))

回答2:

Just plain javascript, no libs:

function foo (folder, enconding) {
    return new Promise(function(resolve, reject) {
        fs.readdir(folder,enconding, function(err, filenames){
            if (err) 
                reject(err); 
            else 
                resolve(filenames);
        });
    });
};

e.g

foo(someFolder, "someEncoding")
.then((files) => console.log(files))
.catch((error) => console.log(error));

回答3:

I figured it out; I just needed to use statSync instead of stat

const fs = require('fs');

var arr = [];

var files = fs.readdirSync(folder);

files.forEach(file => {
  let fileStat = fs.statSync(folder + '/' + file).isDirectory();
  if(!fileStat) {
    arr.push(file);
  }
});

console.log(arr);

回答4:

if you want to use a promise instead of a callback you can promisify fs.

const Promise = require('bluebird');
const fs = Promise.promisifyAll(require('fs'));

fs.readdirAsync('./some').then()

http://bluebirdjs.com/docs/api/promise.promisifyall.html

回答5:

Have you tried fs-extra module?

来源：https://stackoverflow.com/questions/44019316/chaining-fs-readdir-with-a-then-to-return-an-array

标签

javascript

node.js