object set js

let nombres = [10, 45, 75, 10 ,24,45 ] ;
//let monSet = new Set(nombres) ;
let monSet = new Set() ;

monSet.add('100') ;
monSet.add('280') ; 
//monSet.delete('100');

console.log(monSet.size) ;

return Array.from(new Set(this.posts.map(e => e.category)))