client/extensions/woocommerce/state/sites/settings/mailchimp/reducer.js
function apiKeySubmit( state = false, { type } ) {
	switch ( type ) {
		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT:
		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT_SUCCESS:
		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT_FAILURE:
			return WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT === type;
	}

	return state;
}
function apiKeySubmit( state = false, { type } ) {
	switch ( type ) {
		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT:
		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT_SUCCESS:
		case WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT_FAILURE:
			return WOOCOMMERCE_MAILCHIMP_API_KEY_SUBMIT === type;
	}

	return state;
}
Updates state with api key submit status

@param  {Object} state  Current state
@param  {Object} action Action
@return {Object}        Updated state