let persons = [
	{
		name: 'Sergey',
		surname: 'Honcharenko',
		age: 28,
		isMarried: false,
	},
	{
		name: 'Andrew',
		surname: 'Klymchuk',
		middleName: 'Anatoliyovych',
		haveAJob: true,
	},
	{
		name: 'Alexander',
		surname: 'Slobodian',
		sex: 'male',
		hasAPet: false,
	}
]

for (let key in persons) {
	if('name' in persons[key] && 'surname' in persons[key] && 'middleName' in persons[key]) {
		persons[key].fullName = `${persons[key].surname} ${persons[key].name} ${persons[key].middleName}`;
	}
}

console.log(persons);