Angular LocalStorage Service

localstorage.service.ts

import { Injectable } from '@angular/core';

import { APP_CONSTANTS } from '@constants/app.constants';

@Injectable({
    providedIn: 'root'
})
export class LocalStorageService {

    constructor() { }

    static loadInitialState() {
        return Object.keys(localStorage).reduce((state: any, storageKey) => {
            if (storageKey.includes(`_cap_${APP_CONSTANTS.APP_PREFIX}`)) {
                const stateKeys = storageKey
                    .replace(`_cap_${APP_CONSTANTS.APP_PREFIX}`, '')
                    .toLowerCase()
                    .split('.')
                    .map(key =>
                        key
                            .split('-')
                            .map((token, index) =>
                                index === 0
                                    ? token
                                    : token.charAt(0).toUpperCase() + token.slice(1)
                            )
                            .join('')
                    );
                let currentStateRef = state;
                stateKeys.forEach((key, index) => {
                    if (index === stateKeys.length - 1) {
                        currentStateRef[key] = JSON.parse(localStorage.getItem(storageKey));
                        return;
                    }
                    currentStateRef[key] = currentStateRef[key] || {};
                    currentStateRef = currentStateRef[key];
                });
            }
            return state;
        }, {});
    }

    static setItem(key: string, value: any) {
        localStorage.setItem(`_cap_${APP_CONSTANTS.APP_PREFIX}-${key}`, JSON.stringify(value));
    }

    static getItem(key: string) {
        return JSON.parse(localStorage.getItem(`_cap_${APP_CONSTANTS.APP_PREFIX}-${key}`));
    }

    static removeItem(key: string) {
        localStorage.removeItem(`_cap_${APP_CONSTANTS.APP_PREFIX}-${key}`);
    }

    /** Tests that localStorage exists, can be written to, and read from. */
    static testLocalStorage() {
        const testValue = 'testValue';
        const testKey = 'testKey';
        let retrievedValue: string;
        const errorMessage = 'localStorage did not return expected value';

        this.setItem(testKey, testValue);
        retrievedValue = this.getItem(testKey);
        this.removeItem(testKey);

        if (retrievedValue !== testValue) {
            throw new Error(errorMessage);
        }
    }
}