util

Set of functions often needed when using Node.js.

Table of contents

• Presentation
• Example
• Installation
• Terminology
• assertAndNormalizeDirectoryUrl
• assertAndNormalizeFileUrl
• assertDirectoryPresence
• assertFilePresence
• bufferToEtag
• collectFiles
• comparePathnames
• copyFileSystemNode
• ensureEmptyDirectory
• ensureParentDirectories
• fileSystemPathToUrl
• isFileSystemPath
• moveFileSystemNode
• readDirectory
• readFile
• readFileSystemNodeModificationTime
• readFileSystemNodeStat
• readSymbolicLink
• registerDirectoryLifecycle
• registerFileLifecycle
• removeFileSystemNode
• resolveUrl
• urlIsInsideOf
• urlToBasename
• urlToExtension
• urlToFilename
• urlToFileSystemPath
• urlToOrigin
• urlToParentUrl
• urlToPathname
• urlToRelativeUrl
• urlToRessource
• urlToScheme
• writeDirectory
• writeFile
• writeFileSystemNodeModificationTime
• writeSymbolicLink
• Advanced api

Presentation

This repository provides utils functions needed to work with files. It has no external dependency and two preferences:

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

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.

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 module accepts url object since version 7.6 but not url string.

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.

Example

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.

Installation

npm install @jsenv/util

Terminology

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.

fileSystemNode

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

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/.

import { assertAndNormalizeDirectoryUrl } from "@jsenv/util"

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

unit test • implementation

assertAndNormalizeFileUrl

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.

import { assertAndNormalizeFileUrl } from "@jsenv/util"

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

unit test • implementation

assertDirectoryPresence

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.

import { assertDirectoryPresence } from "@jsenv/util"

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

unit test • implementation

assertFilePresence

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.

import { assertFilePresence } from "@jsenv/util"

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

unit test • implementation

bufferToEtag

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.

import { bufferToEtag } from "@jsenv/util"

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

unit test • implementation • Buffer documentation on Node.js • eTag documentation on MDN

collectFiles

collectFiles is an async function collectings a subset of files inside a directory.

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 test • implementation

comparePathnames

comparePathnames is a function compare two pathnames and returning which pathnames comes first in a filesystem.

import { comparePathnames } from "@jsenv/util"

const pathnames = ["a/b.js", "a.js"]
pathnames.sort(comparePathnames)

implementation

copyFileSystemNode

copyFileSystemNode is an async function creating a copy of the filesystem node at a given destination

import { copyFileSystemNode } from "@jsenv/util"

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

unit test • implementation

ensureEmptyDirectory

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.

import { ensureEmptyDirectory } from "@jsenv/util"

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

unit test • implementation

ensureParentDirectories

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.

import { ensureParentDirectories } from "@jsenv/util"

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

implementation

writeDirectory

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.

import { writeDirectory } from "@jsenv/util"

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

unit test • implementation

fileSystemPathToUrl

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.

import { fileSystemPathToUrl } from "@jsenv/util"

fileSystemPathToUrl("/directory/file.js")

unit test • implementation

isFileSystemPath

isFileSystemPath is a function receiving a string and returning a boolean indicating if this string is a filesystem path.

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 test • implementation

moveFileSystemNode

moveFileSystemNode is an async function moving a filesystem node to a destination.

import { moveFileSystemNode } from "@jsenv/util"

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

unit test • implementation

readDirectory

readDirectory is an async function returning an array of string representing all filesystem nodes inside that directory.

import { readDirectory } from "@jsenv/util"

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

implementation

readFileSystemNodeModificationTime

readFileSystemNodeModificationTime is an async function returning a number of milliseconds representing the date when the file was modified.

import { readFileSystemNodeModificationTime } from "@jsenv/util"

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

implementation

readFile

readFile is an async function returning the content of a file as string, buffer, or json.

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 test • implementation

readFileSystemNodeStat

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.

import { readFileSystemNodeStat } from "@jsenv/util"

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

unit test • implementation • stats object documentation on Node.js

readSymbolicLink

readSymbolicLink is an async function returning a symbolic link target as url string.

import { readSymbolicLink } from "@jsenv/util"

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

implementation • symlink documentation on Node.js

registerDirectoryLifecycle

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.

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
unregister()

unit test • implementation

registerFileLifecycle

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.

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
unregister()

unit test • implementation

removeFileSystemNode

removeFileSystemNode is an async function removing a node (directory, file, symbolic link) from the filesystem.

import { removeFileSystemNode } from "@jsenv/util"

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

unit test • implementation

resolveUrl

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.

import { resolveUrl } from "@jsenv/util"

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

unit test • implementation

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:///")

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

urlIsInsideOf is a function returning a boolean indicating if an url is inside an other url.

import { urlIsInsideOf } from "@jsenv/util"

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

unit test • implementation

urlToBasename

urlToBasename is receiving an url and returning its basename.

import { urlToBasename } from "@jsenv/util"

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

unit test • implementation

urlToExtension

urlToExtension is receiving an url and returning its extension.

import { urlToExtension } from "@jsenv/util"

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

unit test • implementation

urlToFilename

urlToFilename is receiving an url and returning its filename.

import { urlToFilename } from "@jsenv/util"

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

unit test • implementation

urlToFileSystemPath

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.

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 test • implementation

urlToOrigin

urlToOrigin is a function receiving an url and returning its origin.

import { urlToOrigin } from "@jsenv/util"

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

unit test • implementation

urlToParentUrl

urlToParentUrl is a function receiving an url and returning its parent url if any or the url itself.

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 test • implementation

urlToPathname

urlToPathname is a function receiving an url and returning its pathname.

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 test • implementation

urlToRelativeUrl

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.

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 test • implementation

urlToRessource

urlToRessource is a function receiving an url and returning its ressource.

import { urlToRessource } from "@jsenv/util"

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

unit test • implementation

urlToScheme

urlToScheme is a function receiving an url and returning its scheme.

import { urlToScheme } from "@jsenv/util"

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

unit test • implementation

writeFile

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.

import { writeFile } from "@jsenv/util"

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

unit test • implementation

writeFileSystemNodeModificationTime

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.

import { writeFileSystemNodeModificationTime } from "@jsenv/util"

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

unit test • implementation

writeSymbolicLink

writeSymbolicLink is an async function writing a symlink link to a file or directory on the filesystem.

import { writeSymbolicLink } from "@jsenv/util"

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

implementation • symlink 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