Origin

Greek ephemeros “lasting only a day”.

Definition

The opposite of persistant.

Data structures are ephemeral because properties can be mutated and there’s no way to get back the original object

const dinner = {
    main: 'turkey',
    side: 'potatoes'
}
 
dinner.side = 'potatoes'
 
console.log(dinner) // { main: 'turkey', side: 'potatoes' }