The Object prototype property allows the addition of new properties and methods to objects.

<!-- html element to place output -->
<p id="my_output"></p>

// function
function my_family(name, title, born) {
    this.name = name;
    this.title = title;
    this.born = born;
}

// prototype
my_family.prototype.allowance = 10;

// variable
const johnny = new my_family('Johnny Shay', 'Child', 2013);

// output to the HTML element
document.getElementById('my_output').innerHTML = johnny.allowance;

10

object.prototype.name = value