valueOf () {
        try {
            return decodeURIComponent(this.value);
        }
        // handle malformed URI sequence
        // refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Malformed_URI
        catch (error) {
            /* istanbul ignore next */
            return this.value;
        }
    }
Get the value of this cookie.

@returns {String}