Helper for working with `window.localStorage`

storage.js

// ================================
// Flag for `localStorage` support.
// ================================

const flag = (() => {
	// Assume no support.
	let bool = false;

	// Used in the `try`.
	const key = 'TEST_KEY';
	const val = 'TEST_VAL';

	// Rigorously test for support.
	try {
		// Set the key/value.
		window.localStorage.setItem(key, val);

		// Are we able to read it?
		bool = window.localStorage.getItem(key) === val;

		// Delete the key/value.
		window.localStorage.removeItem(key);
	} catch (e) {
		bool = false;
	}

	// Return the boolean.
	return bool;
})();

// =======================
// Cache: Alias to object.
// =======================

const hasProp = Object.prototype.hasOwnProperty;

const cacheFallback = {
	clear: function() {
		for (const key in cache) {
			if (key !== 'clear' && hasProp.call(cache, key)) {
				delete cache[key];
			}
		}
	}
};

const cache = flag ? window.localStorage : cacheFallback;

// =======================
// Cache: Clear key/value.
// =======================

const clear = () => {
	cache.clear();
};

// ==============
// Cache: Getter.
// ==============

const get = key => {
	let data = cache[key];

	// Exit, if no data.
	if (!data) {
		return;
	}

	try {
		// Attempt to parse.
		data = JSON.parse(data);
	} catch (e) {
		// Set to original.
		data = cache[key];
	}

	return data;
};

// ==============
// Cache: Setter.
// ==============

const set = (key, data) => {
	if (
		key === 'clear' ||
		key === 'getItem' ||
		key === 'key' ||
		key === 'length' ||
		key === 'removeItem' ||
		key === 'setItem'
	) {
		throw new Error(`Cannot overwrite method: window.localStorage.${key}`);
	}

	if (typeof data === 'object') {
		data = JSON.stringify(data);
	}

	cache[key] = data;
};

// ==========================
// Cache: Remove single item.
// ==========================

const remove = key => {
	delete cache[key];
};

// ==============
// Export object.
// ==============

const storage = {
	clear,
	get,
	remove,
	set
};

// Expose methods.
export { storage };