Simple localStorage function with Cookie fallback for older browsers.

SimpleStore.js

/**
 * Simple [local|session]Storage with Cookie Fallback
 * v.1.2.0
 *
 * USAGE:
 * ----------------------------------------
 * Set New / Modify:
 *   store({
 *    storage: {
 *      key: 'my_key',
 *      value: 'some_value',
 *    },
 *  });
 *
 * Retrieve:
 *   store({
 *    storage: {
 *      key: 'my_key',
 *    },
 *  });
 *
 * Delete / Remove:
 *   store({
 *    storage: {
 *      key: 'my_key',
 *      value: null,
 *    },
 *  });
 *
 */

const store = function store({ storage, cookie = {} }) {
  const key = storage.key;
  const storageType = window[storage.type] || window['sessionStorage'];
  const expirationDays = cookie.expirationDays || void 0;

  let value = storage.value === null ? null : storage.value || void 0;

  // Check for native support
  const hasSupport = () => {
    let isAvailable;

    try {
      const x = '__storage_test__';

      storageType.setItem(x, x);
      storageType.removeItem(x);

      isAvailable = true;
    }
    catch(e) {
      isAvailable = false;
    }

    return isAvailable;
  }

  // If value is detected, set new or modify store
  if (value != null) {
    // Convert object values to JSON
    if (typeof value === 'object') {
      value = JSON.stringify(value);
    }
    // Set the store
    if (hasSupport) { // Native support
      storageType.setItem(key, value);
    } else { // Use Cookie
      createCookie(key, value, expirationDays);
    }
  }

  // No value supplied, return value
  if (value === undefined) {
    let data;

    // Get value
    if (hasSupport) { // Native support
      data = storageType.getItem(key);
    } else { // Use cookie
      data = readCookie(key);
    }

    // Try to parse JSON...
    try {
      data = JSON.parse(data);
    }
    catch(e) {}

    return data;
  }

  // Null specified, remove store
  if (value === null) {
    if (hasSupport) { // Native support
      storageType.removeItem(key);
    } else { // Use cookie
      createCookie(key, '', -1);
    }
  }

  /**
   * Creates new cookie or removes cookie with negative expiration
   * @param  key       The key or identifier for the store
   * @param  value     Contents of the store
   * @param  exp       Expiration - creation defaults to 30 days
   */

  function createCookie(key, value, exp) {
    const date = new Date();
    date.setTime(date.getTime() + (exp * 24 * 60 * 60 * 1000));

    const expires = exp != null ? `; expires=${date.toGMTString()}` : '';

    document.cookie = `${key}=${value}${expires}; path=/`;
  }

  /**
   * Returns contents of cookie
   * @param  key       The key or identifier for the store
   */

  function readCookie(key) {
    const nameEQ = `${key}=`;
    const ca = document.cookie.split(';');

    for (let i = 0, max = ca.length; i < max; i++) {
      let c = ca[i];

      while (c.charAt(0) === ' ') {
        c = c.substring(1, c.length);
      }

      if (c.indexOf(nameEQ) === 0) {
        return c.substring(nameEQ.length, c.length);
      }
    }

    return null;
  }
};