Looping through files in a folder Node.JS

Question

I am trying to loop through and pick up files in a directory, but I have some trouble implementing it. How to pull in multiple files and then move them to another folder?

Answer 1

fs.readdir(path[, options], callback) (which Mikey A. Leonetti used in his answer) and its variants (fsPromises.readdir(path[, options]) and fs.readdirSync(path[, options])) each reads all of a directory's entries into memory at once. That's good for most cases, but if the directory has very many entries and/or you want to lower your application's memory footprint, you could instead iterate over the directory's entries one at a time.

Asynchronously

Directories are async iterable, so you could do something like this:

const fs = require('fs')

async function ls(path) {
  const dir = await fs.promises.opendir(path)
  for await (const dirent of dir) {
    console.log(dirent.name)
  }
}

ls('.').catch(console.error)

Or, you could use dir.read() and/or dir.read(callback) directly.

Synchronously

Directories aren't sync iterable, but you could use dir.readSync() directly. For example:

const fs = require('fs')

const dir = fs.opendirSync('.')
let dirent
while ((dirent = dir.readSync()) !== null) {
  console.log(dirent.name)
}
dir.closeSync()

Or, you could make directories sync iterable. For example:

const fs = require('fs')

function makeDirectoriesSyncIterable() {
  const p = fs.Dir.prototype
  if (p.hasOwnProperty(Symbol.iterator)) { return }
  const entriesSync = function* () {
    try {
      let dirent
      while ((dirent = this.readSync()) !== null) { yield dirent }
    } finally { this.closeSync() }
  }
  if (!p.hasOwnProperty(entriesSync)) { p.entriesSync = entriesSync }
  Object.defineProperty(p, Symbol.iterator, {
    configurable: true,
    enumerable: false,
    value: entriesSync,
    writable: true
  })
}
makeDirectoriesSyncIterable()

And then, you could do something like this:

const dir = fs.opendirSync('.')
for (const dirent of dir) {
  console.log(dirent.name)
}

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Note: "In busy processes, use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete, halting all connections."

References:

• Node.js Documentation: File System: Class fs.Dir
• Node.js source code: fs.Dir
• GitHub: nodejs/node: Issues: streaming / iterative fs.readdir #583