Simple as this : 1 2 3 4 5 6 7 8 9 var isClassic = 'false' ; console.log ( '@@@ UIThemeDisplayed ' + ' {!$User.UIThemeDisplayed}' ); if ( '{!$User.UIThemeDisplayed} ' == 'Theme3' ) { isClassic = 'true' ; } To use visualforce page within Salesforce LEX is to use this url . Some scenario that you might want to apply this is when you want to redirect to Visualforce page in Lightning. 1 /one/one.app#/alohaRedirect/apex/apexpagename?parameter