function isSpringFestival ( ) { const start = new Date ( '2019-02-03 00:00:00' ) ; const end = new Date ( '2019-02-13 00:00:00' ) ; const now = new Date ( ) ; return now < end && now > start ; } export default function springFestivalExtend ( ) { const extraCss = document . querySelector ( '#extraCss' ) ; setTimeout ( ( ) => { if ( isSpringFestival ( ) ) { extraCss [ 'href' ] = './extra/springFestivalTheme/style.css' ; } } , 0 ) ; }