LocalStorage Migrator

This is a library for handling migrations of local storage. It is similar to DbUp. It uses rstolsmark-json-migrator for handling the migration logic.

Install

npm i localstorage-migrator

Usage

A migration is an object that consist of two items:

• name: This has to be unique
• up: a method that is called when applying the migration.

Example:

import * as migrator from "localstorage-migrator";
 
const objectKey = "someKey";
 
const migrations = [
  {
    name: "delta1",
    up: () => {
      localStorage.setItem(
        objectKey,
        JSON.stringify({
          name: "John Doe"
        })
      );
    }
  },
  {
    name: "delta2",
    up: () => {
      var object = JSON.parse(localStorage.getItem(objectKey) as string);
      object.age = 2;
      localStorage.setItem(objectKey, JSON.stringify(object));
    }
  },
  {
    name: "delta3",
    up: () => {
      var object = JSON.parse(localStorage.getItem(objectKey) as string);
      object.age++;
      localStorage.setItem(objectKey, JSON.stringify(object));
    }
  }
];
 
/* This would typically be called in some startup method 
   before local storage is accessed by other code. */
export function runMigrations(): void {
  migrator.migrate(migrations);
}

An example project can be found on GitHub: https://github.com/ragnarstolsmark/migratortest

Methods

migrate

The migrate method takes a an array of migrations, filters them by those who have already been applied and executes them in sequence. The applied migrations is then stored in local storage under a key called: "appliedMigrations".

getAppliedMigrations

This returns an array of those appliedMigrations that have been stored in local storage. They are returned in the order they was applied. An appliedMigration consist of:

• name: The name of the migration that has been applied
• dateApplied: The date the migration was applied

storeAppliedMigrations

This takes an array of appliedMigration objects and stores them in local storage. This can work like a reset method when calling it with an empty array.