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2.3.3 • Public • Published


Simple key-value storage (a persistent data structure) directly on file system, maps each key to a separate file.

  • Simple key-value storage model
  • Very easy to learn and use
  • Both Synchronous and Asynchronous APIs
  • One JSON containing file per each key
  • Built-in configurable cache
  • Both Promise and Callback support
const store = require("key-file-storage")('my/storage/path')

// Write something to file 'my/storage/path/myfile'
store.myfile = { x: 123 }

// Read contents of file 'my/storage/path/myfile'
const x = store.myfile.x

// Delete file 'my/storage/path/myfile'
delete store.myfile

A nice alternative for any of these libraries: node-persist, configstore, flat-cache, conf, simple-store, and more...


Installing package on Node.js:

$ npm install key-file-storage


Initializing a key-file storage:

// ES Modules import style:
import kfs from 'key-file-storage'

// CommonJS import style:
const kfs = require("key-file-storage")

const store = kfs('/storage/directory/path', caching)

The value of caching can be

  1. true (By default, if not specified) : Unlimited cache, anything will be cached on memory, good for small data volumes.

  2. false : No cache, read the files from disk every time, good when other applications can modify the files' contents arbitrarily.

  3. n (An integer number) : Limited cache, only the n latest referred key-values will be cached, good for large data volumes where only a fraction of data is being used frequently .


Synchronous API

As simple as native javascript objects:

store['key'] = value       // Writes file
store['key']               // Reads file
delete store['key']        // Deletes file
delete store['*']          // Deletes all storage files
'key' in store             // Checks for file existence
                           //=> true or false
  • You can use store.keyName instead of store['keyName'] anywhere if the key name allows.

  • undefined is not supported as a savable value, but null is. Saving a key with value undefined is equivalent to removing it. So, you can use store['key'] = undefined or even store['*'] = undefined to delete files.

  • Synchronous API will throw an exception if any errors happen, so you shall handle it your way.

Asynchronous API with Promises

Every one of the following calls returns a promise:

store('key', value)          // Writes file
store('key')                 // Reads file
new store('key')             // Resets/deletes file
new store('*')  /* or */
new store()     /* or */
new store                    // Deletes all storage files
('key' in store(), store())  // Checks for file existence
                             // Resolves to true or false
  • Once again, undefined is not supported as a savable value, but null is. Saving a key with value undefined is equivalent to removing it. So, you can use store('key', undefined) or even store('*', undefined) to delete files.

Asynchronous API with Callbacks

The same as asynchronous with promises, but with callback function as the last input parameter of store() :

store('key', value, cb)   // Writes file
store('key', cb)          // Reads file
new store('key', cb)      // Resets/Deletes file
new store('*', cb)   /* or */
new store(cb)             // Deletes all storage files
'key' in store(cb)        // Checks for file existence
                          // without promise output
                   /* or */
('key' in store(), store(cb))
                          // Checks for file existence
                          // with promise output
  • These calls still return a promise on their output (except for 'key' in store(callback) form of existence check).

  • The first input parameter of all callback functions is err, so you shall handle it within the callback. Reading and Existence checking callbacks provide the return values as their second input parameter.

Folders as Collections

Every folder in the storage can be treated as a collection of key-values.

You can query the list of all containing keys (filenames) within a collection (folder) like this (Note that a collection path must end with a forward slash '/'):

Synchronous API

try {
    const keys = store['col/path/']
    // keys = ['col/path/key1', 'col/path/sub/key2', ... ]
} catch (error) {
    // Handle error...

Asynchronous API with Promises

    .then(keys => {
        // keys = ['col/path/key1', 'col/path/sub/key2', ... ]
    .catch(error => {
        // Handle error...

Asynchronous API with Callbacks

store('col/path/', (error, keys) => {
    if (error) {
        // Handle error...
    // keys = ['col/path/key1', 'col/path/sub/key2', ... ]


  • NOTE 1 : Each key will map to a separate file (using the key itself as its relative path). Therefore, keys may be relative paths, e.g: 'data.json', '/my/key/01' or 'any/other/relative/path/to/a/file'. The only exceptions are the strings including '..' (double dot) which will not be accepted for security reasons.

  • NOTE 2 : You may have hidden key files by simply add a '.' before the filename in the key path.

  • NOTE 3 : If a key's relative path ends with a forward slash '/', it will be considered to be a collection (folder) name. So, 'data/set/' is a collection and 'data/set/key' is a key in that collection.

  • NOTE 4 : This module has a built-in implemented cache, so, when activated, accessing a certain key more than once won't require file-system level operations again for that file.

  • NOTE 5 : When activated, caching will include queries on collections too.


import kfs from "key-file-storage"

// Locate 'db' folder in the current directory as the storage path,
// Require 100 latest accessed key-values to be cached:
const store = kfs('./db', 100)

// Create file './db/users/hessam' containing this user data, synchronously: 
store['users/hessam'] = ({
    name: "Hessam",
    skills: {
        java: 10,
        csharp: 15

// Read file './db/users/hessam' as a JSON object, asynchronously:
store('users/hessam').then(hessam => {
    console.log(`Hessam's java skill is ${}.`)

// Check whether file './db/users/mahdiar' exists or not, asynchronously:
'users/mahdiar' in store((error, exists) => {
    if (exists) {
        console.log("User Mahdiar exists!")

// List all the keys in './db/users/', synchronously:
const allUsers = store['users/']
//=> ['users/hessam', 'users/mahdiar', ... ]


It would be very appreciated if you had any suggestions or contribution on this repository or submitted any issue.

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