W-Mills

const foo = {
  bar: 'baz',
  getBar: function() {     // assigned as a property on an object, getBar is a method
    console.log(this.bar); // the value of this here: foo
  },
};

foo.getBar()               // logs 'baz'

let qux = foo.getBar;      // assigning the function getBar to the variable qux

W-Mills

const foo = {
  bar: 'baz',
  getBar: function() {      
    console.log(this.bar);  
  },
};              

let qux = foo.getBar;     

qux.call(foo);             // logs 'baz'

W-Mills

const foo = {
  bar: 10,
  multiplyByBar: function(...args) {
    args.forEach(arg => console.log(arg * this.bar));
  },
};

foo.multiplyByBar(5);        // logs 50
foo.multiplyByBar(5, 10, 15) // logs 50, then 100, then 150

W-Mills

const foo = {
  bar: 10,
  multiplyByBar: function(...args) {
    args.forEach(function(arg) {
      console.log(arg * this.bar);
    }, this);
  }
};

const qux = foo.multiplyByBar.bind(foo);

W-Mills

const foo = {
  bar: 10,
  multiplyByBar: function(...args) {
    args.forEach(arg => console.log(arg * this.bar)); // arrow function does not change the context
  }
};

const qux = foo.multiplyByBar.bind(foo);

qux(5);           // logs 50