types & grammer

var s = 'abc';
s[1] = 'B';

console.log(s);

var l = new String('abc');
l[1] = 'B';
console.log(l);

0.1 + 0.2 === 0.3;
0.8 - 0.6 === 0.3;

Array.isArray(Array.prototype)

Boolean(Boolean(false));
Boolean(document.all);

[] == '';
[3] == 3;
[] == false;
42 == true;

var a = 3;
let a;

var b = 3;

function foo( a = 42, b = a + b + 5 ) {
    // ..
}

foo()

scope & closures

var scope = 'global scope';
function checkscope () {
  var scope = 'local scope';
  function f() {
    return scope; 
  }
  return f;
}

console.log(a);
var a = 3;

var foo = 1;
function foo () {

}
console.log(foo);

var foo = 1;
(function () {
  foo = 2;
  function foo () {
     
  }

  console.log(foo);
})()

console.log(foo);

for (var i = 0; i < 10; i++) {
  setTimeout(function () {
    console.log(i);
  }, i * 1000)
}

function foo() {
  "use strict";
  console.log( this.a );
}

var a = 2;

foo();

"use strict";
var a = 2;

console.log(this);

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

var a = 2;

(function(){
	"use strict";

	foo(); // 2
})();

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

const o1 = { a: 3 };
const o2 = { a: 4 };

foo.bind(o1).bind(o2)();

function F () {
  this.a = 3;
  return {
    a: 4;
  }
}

const f = new F();
console.log(f.a);