enum.js

let obj = {
    a: 1,
    b: 2
 }
Object.defineProperty(obj, 'a', {
    enumerable: false
})
 
for (let key in obj){
    console.log(key) // b
}
 
 console.log( Object.keys(obj))  // [ 'b' ]
 
 console.log(Object.getOwnPropertyNames(obj)) // [ 'a', 'b' ]