enumeration2.js

const properties = Object.keys(user);

// length = len
let i, len;
for (i=0, len=properties.length; i<len; i++) {
  console.log("Name: " + properties[i]); // Name: firstName,  Name: showDetails
  console.log("Value: " + user[properties[i]]); // Value: Akash,  Value: function ()
}

console.log(properties) // [ 'firstName', 'showDetails' ]

// Custom Property in user
console.log("firstName" in user); // true 
console.log(user.propertyIsEnumerable("firstName")) // true (because it is listed in Object.keys())

// Inherited Property
console.log("length" in properties); // true 
console.log(properties.propertyIsEnumerable("length")) // false