Set of functions often needed when using Node.js.

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Set of functions often needed when using Node.js.
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Table of contents
This repository provides utils functions needed to work with files. It has no external dependency and two preferences:
prefer url over filesystem path
An url is better than a filesystem path because it does not care about the underlying filesystem format.
  • A file url: file:///directory/file.js
  • A Windows file path: C:\\directory\\file.js
  • A Linux file path: /directory/file.js

prefer url string over url object
There is a deliberate preference for url string over url object in the documentation and codebase.
const urlString = "file:///directory/file.js"
const urlObject = new URL("file:///directory/file.js")

A string is a simpler primitive than an url object and it becomes important while debugging.
Screenshot of an url object while debugging
screenshot of url object while debugging in vscode

Screenshot of an url string while debugging
screenshot of url string while debugging in vscode

This repository also provides some utils around urls not provided by Node.js. For instance it exports urlToRelativeUrl which can be seen as the equivalent of path.relative for urls.
Finally exported functions fully support url, even url string while native fs module does not.
fs lack support for url string
fs module accepts url object since version 7.6 but not url string.
screenshot of readFile documentation changelog
Passing an url string to a function from fs will always throw ENOENT error.
import { readFileSync } from "fs"

readFileSync(import.meta.url) // throw ENOENT

const { readFileSync } = require("fs")

readFileSync(`file://${__filename}`) // throw ENOENT

Node.js made this choice for performance reasons but it hurts my productivity.

The code below is a basic example reading package.json file as buffer.
import { readFileSync } from "fs"
import { resolveUrl, urlToFileSystemPath } from "@jsenv/util"

const packageFileUrl = resolveUrl("package.json", import.meta.url)
const packageFilePath = urlToFileSystemPath(packageFileUrl)
const packageFileBuffer = readFileSync(packageFilePath)

With times more functions were added, all util are documented a bit further.
npm install @jsenv/util
This documentation and source code uses some wording explained in this part.

Urls parts

You can refer to figure below to see how each part of an url is named.
                origin                                                                                     │
      ┌────────────┴──────────────┐                                                                        │
      │                       authority                                                                    │
      │           ┌───────────────┴───────────────────────────┐                                            │
      │           │                                         host                                        ressource
      │           │                                ┌──────────┴────────────────┐             ┌──────────────┴────────┬────────┐
      │           │                             hostname                       │          pathname                   │        │
      │           │                 ┌──────────────┴────────────┐              │      ┌──────┴──────┐                │        │
protocol userinfo subdomain domain │ │ filename │ │
┌─┴──┐     ┌───┴────┐            │                  ┌────────┴───────┐      │      │         ┌───┴─────┐          │        │
scheme │username password lowerleveldomains secondleveldomain topleveldomain port dirname basename extension search hash ┌──┴───┐│┌──┴───┐ ┌──┴───┐ ┌──┬─┬─┴─────┬───┐┌───────┴───────┐ ┌──────┴──────┐┌┴┐┌────┴─────┐ ┌──┴───┐ ┌───┴───┐ ┌────┴────┐ ┌┴┐ │ │││ │ │ │ │ │ │ │ ││ │ │ ││ ││ │ │ │ │ │ │ │ │ │ scheme://username:password@test.abcdedgh.www.secondleveldomain.topleveldomain:123/hello/world/basename.extension?name=ferret#hash


fileSystemNode word is used when a function does not assume what it is going to interact with: file, directory, or something else. For example copyFileSystemNode(fromUrl, toUrl, options) will take whatever is at fromUrl and copy it at toUrl.
assertAndNormalizeDirectoryUrl is a function ensuring the received value can be normalized to a directory url string. This function is great to make a function accept various values as directory url and normalize it to a standard directory url like file:///directory/.
assertAndNormalizeDirectoryUrl code example
import { assertAndNormalizeDirectoryUrl } from "@jsenv/util"

assertAndNormalizeDirectoryUrl("/directory") // file:///directory/
assertAndNormalizeDirectoryUrl("C:\\directory") // file://C:/directory/

unit testimplementation
assertAndNormalizeFileUrl is a function ensuring the received value can be normalized to a file url string. This function is great to make a function accept various values as file url and normalize it to a standard file url like file:///directory/file.js.
assertAndNormalizeFileUrl code example
import { assertAndNormalizeFileUrl } from "@jsenv/util"

assertAndNormalizeFileUrl("/directory/file.js") // file:///directory/file.js
assertAndNormalizeFileUrl("C:\\directory\\file.js") // file:///C:/directory/file.js

unit testimplementation
assertDirectoryPresence is an async function throwing if directory does not exists on the filesystem. This function is great when code expects a directory to exist before going further.
assertDirectoryPresence code example
import { assertDirectoryPresence } from "@jsenv/util"

await assertDirectoryPresence("file:///Users/directory/")

unit testimplementation
assertFilePresence is an async function throwing if a file does not exists on the filesystem. This function is great to when code expects a file to exist before going further.
assertFilePresence code example
import { assertFilePresence } from "@jsenv/util"

await assertFilePresence("file:///Users/directory/file.js")

unit testimplementation
bufferToEtag is a function receiving a buffer and converting it into an eTag. This function returns a hash (a small string) representing a file content. You can later check if the file content has changed by comparing a previously generated eTag with the current file content.
bufferToEtag code example
import { bufferToEtag } from "@jsenv/util"

const eTag = bufferToEtag(Buffer.from("Hello world"))
const otherEtag = bufferToEtag(Buffer.from("Hello world"))
eTag === otherEtag // true

unit testimplementationBuffer documentation on Node.jseTag documentation on MDN
collectFiles is an async function collectings a subset of files inside a directory.
collectFiles code example
import { collectFiles } from "@jsenv/util"

const files = await collectFiles({
  directoryUrl: "file:///Users/you/directory",
  structuredMetaMap: {
    whatever: {
      "./**/*.js": 42,
  predicate: (meta) => {
    return meta.whatever === 42

unit testimplementation
comparePathnames is a function compare two pathnames and returning which pathnames comes first in a filesystem.
comparePathnames code example
import { comparePathnames } from "@jsenv/util"

const pathnames = ["a/b.js", "a.js"]

copyFileSystemNode is an async function creating a copy of the filesystem node at a given destination
copyFileSystemNode code example
import { copyFileSystemNode } from "@jsenv/util"

await copyFileSystemNode(`file:///file.js`, "file:///destination/file.js")
await copyFileSystemNode(`file:///directory`, "file:///destination/directory")

unit testimplementation
ensureEmptyDirectory is an async function ensuring a directory is empty. It removes a directory content when it exists or create an empty directory. This function was written for testing. It is meant to clean up a directory in case a previous test execution let some files and you want to clean them before running your test.
ensureEmptyDirectory code example
import { ensureEmptyDirectory } from "@jsenv/util"

await ensureEmptyDirectory(`file:///directory`)

unit testimplementation
ensureParentDirectories is an async function creating every directory leading to a file. This function is useful to ensure a given file directories exists before doing any operation on that file.
ensureParentDirectories code example
import { ensureParentDirectories } from "@jsenv/util"

await ensureParentDirectories(`file:///directory/subdirectory/file.js`)

writeDirectory is an async function creating a directory on the filesystem. writeDirectory is equivalent to fs.promises.mkdir but accepts url strings as directory path.
writeDirectory code example
import { writeDirectory } from "@jsenv/util"

await writeDirectory(`file:///directory`)

unit testimplementation
fileSystemPathToUrl is a function returning a filesystem path from an url string. fileSystemPathToUrl is equivalent to pathToFileURL from Node.js but returns string instead of url objects.
fileSystemPathToUrl code example
import { fileSystemPathToUrl } from "@jsenv/util"


unit testimplementation
isFileSystemPath is a function receiving a string and returning a boolean indicating if this string is a filesystem path.
isFileSystemPath code example
import { isFileSystemPath } from "@jsenv/util"

isFileSystemPath("/directory/file.js") // true
isFileSystemPath("C:\\directory\\file.js") // true
isFileSystemPath("directory/file.js") // false
isFileSystemPath("file:///directory/file.js") // false

unit testimplementation
moveFileSystemNode is an async function moving a filesystem node to a destination.
moveFileSystemNode code example
import { moveFileSystemNode } from "@jsenv/util"

await moveFileSystemNode("file:///file.js", "file:///destination/file.js")
await moveFileSystemNode("file:///directory", "file:///destination/directory")

unit testimplementation
readDirectory is an async function returning an array of string representing all filesystem nodes inside that directory.
readDirectory code example
import { readDirectory } from "@jsenv/util"

const content = await readDirectory("file:///directory")

readFileSystemNodeModificationTime is an async function returning a number of milliseconds representing the date when the file was modified.
readFileSystemNodeModificationTime code example
import { readFileSystemNodeModificationTime } from "@jsenv/util"

const mtimeMs = await readFileSystemNodeModificationTime("file:///directory/file.js")

readFile is an async function returning the content of a file as string, buffer, or json.
readFile code example
import { readFile } from "@jsenv/util"

const fileContentAsString = await readFile("file:///directory/file.json")
const fileContentAsBuffer = await readFile("file:///directory/file.json", { as: "buffer" })
const fileContentAsJSON = await readFile("file:///directory/file.json", { as: "json" })

unit testimplementation
readFileSystemNodeStat is an async function returning a filesystem node stats object. readFileSystemNodeStat is equivalent to fs.promises.stats from Node.js but accepts url strings as file path.
readFileSystemNodeStat code example
import { readFileSystemNodeStat } from "@jsenv/util"

const stats = await readFileSystemNodeStat("file:///directory/file.js")

unit testimplementationstats object documentation on Node.js
readSymbolicLink is an async function returning a symbolic link target as url string.
readFileSystemNodeStat code example
import { readSymbolicLink } from "@jsenv/util"

const targetUrlOrRelativeUrl = await readSymbolicLink("file:///directory/link")

implementationsymlink documentation on Node.js
registerDirectoryLifecycle is a function watching a directory at a given path and calling added, updated, removed according to what is happening inside that directory. Usually, filesystem takes less than 100ms to notify something has changed.
registerDirectoryLifecycle code example
import { registerDirectoryLifecycle } from "@jsenv/util"

const contentMap = {}
const unregister = registerDirectoryLifecycle("file:///directory", {
  added: ({ relativeUrl, type }) => {
    contentMap[relativeUrl] = type
  removed: ({ relativeUrl }) => {
    delete contentMap[relativeUrl]

// you can call unregister when you want to stop watching the directory

unit testimplementation
registerFileLifecycle is a function watching a file and calling added, updated, removed according to what is happening to that file. Usually, filesystem takes less than 100ms to notify something has changed.
registerFileLifecycle code example
import { readFileSync } from "fs"
import { registerFileLifecycle } from "@jsenv/file-watcher"

const filePath = "/file.config.json"
let currentConfig = null
const unregister = registerFileLifecycle(filePath, {
  added: () => {
    currentConfig = JSON.parse(String(readFileSync(filePath)))
  updated: () => {
    currentConfig = JSON.parse(String(readFileSync(filePath)))
  removed: () => {
    currentConfig = null
  notifyExistent: true,

// you can call unregister() when you want to stop watching the file

unit testimplementation
removeFileSystemNode is an async function removing a node (directory, file, symbolic link) from the filesystem.
removeFileSystemNode code example
import { removeFileSystemNode } from "@jsenv/util"

await removeFileSystemNode("file:///file.js")
await removeFileSystemNode("file:///directory")

unit testimplementation
resolveUrl is a function receiving two arguments called specifier and baseUrl. Both arguments are required. resolveUrl applies url resolution between specifier and baseUrl and returns the corresponding absolute url string.
resolveUrl code example
import { resolveUrl } from "@jsenv/util"

resolveUrl("file.js", "file:///directory/") // file:///directory/file.js

unit testimplementation

Note about url resolution and directory
When working with directory urls, it is important to have a trailing /.
new URL("foo.js", "file:///dir").href // file:///foo.js
new URL("foo.js", `file:///dir/`).href // file:///dir/foo.js

For this reason, if you have a variable holding a directory url, be sure to put a trailing slash.
import { resolveUrl } from "@jsenv/util"

const directoryUrl = resolveUrl("./dir/", "file:///")

Difference between resolveUrl and URL
Using resolveUrl means code wants to perform url resolution between something that can be relative: specifier, and something absolute: baseUrl.
For this reason resolveUrl will throw if baseUrl is undefined. This is a major difference with URL constructor that would not throw in such case.
import { resolveUrl } from "@jsenv/util"

new URL("http://example.com", undefined) // does not throw

resolveUrl("http://example.com", undefined) // throw "baseUrl is missing to resolve http://example.com"

Technically, http://example.com is already absolute and does not need a baseUrl to be resolved. But, receiving undefined when an absolute url was expected indicates there is something wrong in the code.
This is a feature that helps to catch bugs.
urlIsInsideOf is a function returning a boolean indicating if an url is inside an other url.
urlIsInsideOf code example
import { urlIsInsideOf } from "@jsenv/util"

urlIsInsideOf("file:///directory/file.js", "file:///directory/") // true
urlIsInsideOf("file:///file.js", "file:///directory/") // false

unit testimplementation
urlToBasename is receiving an url and returning its basename.
urlToBasename code example
import { urlToBasename } from "@jsenv/util"

urlToBasename("file:///directory/file.js") // "file"
urlToBasename("file:///directory/") // "directory"
urlToBasename("http://example.com") // ""

unit testimplementation
urlToExtension is receiving an url and returning its extension.
urlToExtension code example
import { urlToExtension } from "@jsenv/util"

urlToExtension("file:///directory/file.js") // ".js"
urlToExtension("file:///directory/file.") // "."
urlToExtension("http://example.com/file") // ""

unit testimplementation
urlToFilename is receiving an url and returning its filename.
urlToFilename code example
import { urlToFilename } from "@jsenv/util"

urlToFilename("file:///directory/file.js") // "file.js"
urlToFilename("file:///directory/file.") // "file."
urlToFilename("http://example.com/file") // "file"

unit testimplementation
urlToFileSystemPath is a function returning a filesystem path from an url. urlToFileSystemPath is equivalent to pathToFileURL from Node.js but returns string instead of url objects.
urlToFileSystemPath code example
import { urlToFileSystemPath } from "@jsenv/util"

// on mac or linux
urlToFileSystemPath("file:///directory/file.js") // /directory/file.js

// on windows
urlToFileSystemPath("file://C:/directory/file.js") // C:\\directory\\file.js

unit testimplementation
urlToOrigin is a function receiving an url and returning its origin.
urlToOrigin code example
import { urlToOrigin } from "@jsenv/util"

urlToOrigin("file:///directory/file.js") // "file://"
urlToOrigin("http://example.com/file.js") // "http://example.com"

unit testimplementation
urlToParentUrl is a function receiving an url and returning its parent url if any or the url itself.
urlToParentUrl code example
import { urlToParentUrl } from "@jsenv/util"

urlToParentUrl("http://example.com/dir/file.js") // "http://example.com/dir/"
urlToParentUrl("http://example.com/dir/") // "http://example.com/"
urlToParentUrl("http://example.com/") // "http://example.com/"

unit testimplementation
urlToPathname is a function receiving an url and returning its pathname.
urlToPathname code example
import { urlToPathname } from "@jsenv/util"

urlToPathname("http://example.com/dir/file.js") // "/dir/file.js"
urlToPathname("http://example.com/dir/") // "/dir/"
urlToPathname("http://example.com/") // "/"

unit testimplementation
urlToRelativeUrl is a function receiving two absolute urls and returning the first url relative to the second one. urlToRelativeUrl is the url equivalent to path.relative from Node.js.
urlToRelativeUrl code example
import { urlToRelativeUrl } from "@jsenv/util"

urlToRelativeUrl("file:///directory/file.js", "file:///directory/") // file.js
urlToRelativeUrl("file:///directory/index.js", "file:///directory/foo/file.js") // ../index.js

unit testimplementation
urlToRessource is a function receiving an url and returning its ressource.
urlToRessource code example
import { urlToRessource } from "@jsenv/util"

urlToRessource("http://example.com/dir/file.js?foo=bar#10") // "/dir/file.js?foo=bar#10"

unit testimplementation
urlToScheme is a function receiving an url and returning its scheme.
urlToScheme code example
import { urlToScheme } from "@jsenv/util"

urlToScheme("http://example.com") // "http"
urlToScheme("file:///dir/file.js") // "file"
urlToScheme("about:blank") // "about"

unit testimplementation
writeFile is an async function writing file and its content on the filesystem. This function auto create file parent directories if they do not exists.
writeFile code example
import { writeFile } from "@jsenv/util"

await writeFile("file:///directory/file.txt", "Hello world")

unit testimplementation
writeFileSystemNodeModificationTime is an async function writing file and its content on the filesystem. writeFileSystemNodeModificationTime is like fs.promises.utimes but accepts url strings as file path.
writeFileSystemNodeModificationTime code example
import { writeFileSystemNodeModificationTime } from "@jsenv/util"

await writeFileSystemNodeModificationTime("file:///directory/file.js", Date.now())

unit testimplementation
writeSymbolicLink is an async function writing a symlink link to a file or directory on the filesystem.
writeSymbolicLink code example
import { writeSymbolicLink } from "@jsenv/util"

await writeSymbolicLink("file:///foo.js", "./bar.js")

implementationsymlink documentation on Node.js
Advanced api
There is a few more functions but they are more specific, you probably don't need them: Advanced api