Standard function prototype

Start by defining a Foo function that we'll use as a constructor.

function Foo (){}

By editing Foo.prototype, we can define properties and methods that will be shared by all instances of Foo.

Foo.prototype.bar = function() {
  return 'I am bar';
};

We can then create an instance using the new keyword, and call the method.

var foo = new Foo();

console.log(foo.bar()); // logs `I am bar`