localStorage helper (takes care of casting types)

local-storage-helper.js

/**
 * local storage helper (takes care of casting types)
 */
var localStorageHelper = {

    /**
     * Check if item exists in local storage.
     * @param {string} key - variable name
     * @return {boolean} true if key exists, otherwise false
     */
    exists: function (key) {
        return Object.prototype.hasOwnProperty.call(localStorage, key);
    },

    /**
     * Get an item from local storage
     * @param {string} key - variable name
     * @return {any} correctly cast value if it exists
     */
    get: function (key) {

        // always get value as a string
        var value = String(localStorage.getItem(key));

        if (value === 'null') return null;

        if (value === 'undefined') return undefined;

        // if it's a float
        if (/^[0-9.]+$/.test(value)) return parseFloat(value);

        // if it's an integer
        if (/^[-0-9]+$/.test(value)) return parseInt(value, 10);
        
        // if it's a boolean
        if (value === 'true' || value === 'false') return (value === 'true');

        // if it's a JSON object
        if (value[0] === '{' || value[0] === '[') {
            try {
                var parsed = JSON.parse(value);
                if (typeof parsed === 'object' || Array.isArray(parsed)) {
                    return parsed;
                }
            } catch (e) {
                // Not a JSON object or array
            }
        }

        return value;
    },

    /**
     * Save an item to local storage
     * @param {string} key - variable name
     * @param {any} value - value of variable to save
     * @return {void}
     */
    set: function (key, value) {

        if (typeof key !== 'string') {
            throw new TypeError('localStorage: Key must be a string');
        }

        if (typeof value === 'object' || Array.isArray(value)) {
            value = JSON.stringify(value);
        }

        localStorage.setItem(key, value);
    },

    /**
     * Remove an item from local storage
     * @param {string} key - variable name
     * @return {void}
     */
    remove: function (key) {
        localStorage.removeItem(key);
    },
    
    /**
     * Clear all local storage values
     * @return {void}
     */
    clear: function () {
        localStorage.clear();
    }
};