input.js

var a = {prime: 1};
var b = {nonprime: 2, prime: 3};
var c = {nonprime: 4, prime: 5, hoge: 6};
var d = Object.assign(a, b, c);
console.log(a);
console.log(b);
console.log(c);
console.log(d);

output

{ prime: 5, nonprime: 4, hoge: 6 }
{ nonprime: 2, prime: 3 }
{ nonprime: 4, prime: 5, hoge: 6 }
{ prime: 5, nonprime: 4, hoge: 6 }