bind.js

function Foo(value) {
  this.value = value;
  
  this.bar = function() {
    return this.value;
  }
  
  this.baz = () => {
    return this.value;
  }
}

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

const bar = foo.bar;
const baz = foo.baz;

// bar: undefined
console.log('bar:', bar());

// baz: Hello world!
console.log('baz:', baz());