A Simple JSON Backed Database in Typescript

07 July 2022

Updated: 03 September 2023

Define the database

The database is defined as a class which has an in-memory store data and a persist method that allows for persisting the database to a file as well as content when an instance is created from an existing JSON file

The code for the database can be seen below:

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import { existsSync, readFileSync, writeFileSync } from 'fs'
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export class Database<TData> {
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  public data: TData
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  constructor(private readonly dbPath: string, initial: TData) {
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    this.data = this.load(initial)
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  }
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  public update = (data: Partial<TData>) =>
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    (this.data = { ...this.data, ...data })
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  public commit = () => this.persist(this.data)
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  private persist = (data: TData) =>
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    writeFileSync(this.dbPath, JSON.stringify(data))
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  private read = (): TData =>
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    JSON.parse(readFileSync(this.dbPath).toString()) as TData
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  private load = (initial: TData): TData => {
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    if (!existsSync(this.dbPath)) {
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      this.persist(initial)
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    }
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    const current = this.read()
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    return {
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      ...initial,
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      ...current,
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    }
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  }
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}

Usage

The database can be used by creating an instance and modifying the data in it by using the update method, and can be written to a file using the commit method:

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import { Database } from './db'
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interface User {
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  name: string
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  age: number
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}
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interface DB {
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  users: User[]
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}
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const initial: DB = {
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  users: [],
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}
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const db = new Database<DB>('./data.json', initial)
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db.update({
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  users: [
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    {
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      name: 'Test',
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      age: 20,
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    },
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  ],
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})
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db.commit()

Functional Example

The above code is found in the below REPL as a runnable example: