Example 1: get index of element in array js const beasts = [ 'ant' , 'bison' , 'camel' , 'duck' , 'bison' ] ; console . log ( beasts . indexOf ( 'bison' ) ) ; // expected output: 1 // start from index 2 console . log ( beasts . indexOf ( 'bison' , 2 ) ) ; // expected output: 4 console . log ( beasts . indexOf ( 'giraffe' ) ) ; // expected output: -1 //*** Thanks to MDN Web Docs ***// //https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/indexOf Example 2: js array return only certain positions const every_nth = ( arr , nth ) => arr . filter ( ( e , i ) => i % nth == = nth - 1 ) ; console . log ( every_nth ( [ 1 , 2 , 3 , 4 , 5 , 6 ] , 1 ) ) ; console . log ( every_nth ( [ 1 , 2 , 3 , 4 , 5 , 6 ] , 2 ) ) ; console . log ( every_nth ( [ 1 , 2 , 3 , 4 , 5 , 6 ] , 3 ) ) ; console . log ( every_nth ( [ 1 , 2 , 3 , 4 , 5 , 6 ] ,...