binding.js

function Foo(value) {
  this.value = value;
}

Foo.prototype.bar = function () {
  function someCall() {
    return this.value;
  }
  
  const anotherCall = () => {
    return this.value;
  }
  
  console.log('someCall()', someCall());
  console.log('anotherCall()', anotherCall());
}

const foo = new Foo('Hello world!');

foo.bar();

const yetAnotherCall = foo.bar;

yetAnotherCall();