How to change a property on an object without mutating it?

Question

const a = {x: "Hi", y: "Test"}
const b = ???
// b = {x: "Bye", y: "Test"}
// a = {x: "Hi", y: "Test"}
         


        

Answer 1

Es6 has a built in function for copying object properties, Object.assign

const b = Object.assign({}, a, {x: 'Bye'})

here we create an empty object, push all of as key value pairs in, followed by the new key value pairs we want to over write. because the empty object is the first argument, we mutate that object, not a