WebStorage Decorators

A Javascript library that adds property decorators to sync a class property with the local or session storage. Useful for persisting themes or local settings over reloads or maintaining filters/search options in the current user session.

Quick Setup

1. Install with: npm install --save webstorage-decorators
2. Add the decorator to your property and use as normal!

import {LocalStorage, SessionStorage} from 'webstorage-decorators';

export class MyCustomClass {
    @LocalStorage({key: 'site_theme', default: 'light_theme'}) theme: string;
    @SessionStorage({encryptWith: config.entryptionKey}) thisUser: User;
    
    constructor() {
       console.log(this.theme, localStorage.getItem('theme')); // Output: 'light_theme', 'light_theme'
       console.log(this.user, localStorage.getItem('user')); // Output: null, undefined
       user = {first: 'John', last: 'Smith', ...}
       console.log(this.user, this.user == localStorage.getItem('user')); // Output: {first: 'John', last: 'Smith', ...}, true
   }
}

Caveats

Custom Functions

You can technically store anything inside local/session storage however everything is serialized using javascript's JSON, so anything extra (prototypes, functions, etc) will be lost. However if you provide a default value, it will be copied & the data injected, giving you a workaround to accessing static properties (Does not work with arrays).

class Person {
    constructor(public first: string, public last: string) { }
    fullName() { return `${this.last}, ${this.first}`; }
}

LocalStorage.setItem('example', '{"first": "John", "last": "Smith"}');
@LocalStorage(null) example!: Person;
console.log(example.fullName()) // ERROR: fullName function doesn't exist

LocalStorage.setItem('example2', '{"first": "John", "last": "Smith"}');
@LocalStorage(new Person(null, null)) example2!: Person;
console.log(example2.fullName()) // Works because we have a default object to copy type from

Impure Functions

Impure functions don't use the Object's setter preventing the storage from being updated. To prevent this use a pure function or save it manually by reading the variable. (Reading triggers change detection & save if there are differences)

@LocalStorage([1, 2]) example: number[];
example.push(3) // Impure & won't update storage
console.log(localStorage.getItem('example')) // Output: [1, 2];
example; // Trigger save
console.log(localStorage.getItem('example')) // Output: [1, 2, 3];

// OR

example = example.concat([3]); // Pure function requires you to use the setter triggering automatic saving