JSFiddle - React, Tailwind, and code Playground

JavaScript

var john_5_years_ago = {
    name: "john",
    company: "google",
    languages: ["c++", "java"]
}

var john_now = {
    name: "john",
    company: "facebook",
    nation: "US",
    languages: ["python", "java", "javascript"]
}

$.each(john_now, function(i, key){
	if(i === 'languages'){
  	$.each(john_5_years_ago[i], function(j){
    	if(john_now[i].indexOf(john_5_years_ago[i][j]) == -1)
      	john_now[i].push(john_5_years_ago[i][j])	
    });
  }
});

console.log(john_now);