function zzz() {
  console.log(this.a);
}

var foo = {
  a: 20,
  bar: zzz,
  bla: function() {
    console.log(this.a);
  }
}

foo.bar() // 20
foo.bla() // 20

var b = 100;

this.blabla = foo.bar;
this.blabla(); // 100

function foo() {
  console.log(this);
}

var obj = { name: 'jigeol' };
foo.call(obj);

function foo(a) {
  this.a = a;
  this.b = 20;
}

var bar = new foo(2);

function foo(bar) {
  this.a = bar;
}

var obj1 = {
  foo: foo
}

obj1.foo(2) // 암시적 바인딩
console.log(obj1.a) // 2

var obj2 = {};

obj1.foo.call(obj2, 3); // 암시적 바인딩한 후 obj2라고 명시적 바인딩
console.log(obj1.a) // 2
console.log(obj2.a) // 3

var obj3 = new obj1.foo(10) // new 바인딩
console.log(obj1.a) // 2
console.log(obj2.a) // 3
console.log(obj3.a) // 10

function foo(something) {
  this.a = something;
}

var obj1 = {};

var bar = foo.bind(obj1); // 명시적 바인딩
bar(2);
console.log(obj1.a); // 2

var baz = new bar(3); // new 바인딩
console.log(obj1.a); // 2
console.log(baz.a); // 3

var a = 10;
var b = 20;
var obj = {
  a: 1,
  func: () => console.log(this.a)
}

obj.func(); // 10

// Arror Function
function test() {
  console.log(this);
  return () => console.log(this.b);
}

var f1 = test();
f1(); // 20
var context = { b: 999 };
var f2 = test.call(context);
f2(); // 999

// function()
function test2() {
  console.log(this);
  return funtion() {
    console.log(this.b);
  }
}

var f3 = test2();
f3(); // 20
var f4 = test2.call(context);
f4(); // 20

<section class="container">
  <div class="inner">
    <button class="close">버튼이에용</button>
  </div>
</section>

document.getElementsByClassName("container").addEventListener('click', () => {
  console.log("I'm container!");
})

document.getElementsByClassName("inner").addEventListener('click', () => {
  console.log("I'm inner!");
})

document.getElementsByClassName("close").addEventListener('click', () => {
  console.log("I'm close button!");
})

I'm close button!
I'm inner!
I'm container!

document.getElementsByClassName("container").addEventListener('click', () => {
  console.log("I'm container!");
}, true)

I'm container!
I'm close button!
I'm inner!