1kohei1

if (DEBUG) { console.log('Debugging is starting'); }
// Results the reference error when debug.js is not loaded.

if (typeof DEBUG !== 'undefined' && DEBUG) { console.log('Debuggins is starting'); }
// This is safer. 

1kohei1

function a() {}
var b = function() {}
typeof a; 'function'
typeof b; 'function'

1kohei1

for (let c in b) { console.log( c ); }; // a
// Enumerable travels prototype chains. 
for (let key in Object.keys( b )) { console.log( key ) }; // nothing prints out

1kohei1

var a = { a: 2, }
var b = Object.create( a );
console.log( b ); // {}
console.log( b.a ); // 2 <- It got 2 from b's prototype chain
/*
b with prototypes
{
	__proto__: {
		a: 2,
		__proto__: { ... }

1kohei1

function mixin(sourceObj, targetObj) {
	for (var key in sourceObj) {
		if (!(key in targetObj)) {
			targetObj[key] = sourceObj[key];
		}
	}
	return targetObj;
}
var Vehicle = {
	engines: 1,

1kohei1

class A {
	public void ignition() {
		System.out.println("A ignition");
	}
	public void drive() {
		this.ignition();
		System.out.println("A drive");
	}
}
class B extends A {

1kohei1

var myObject = {
	a: 2,
	b: 3,
};
Object.defineProperty(myObject, Symbol.iterator, {
	enumerable: false,
	writable: false,
	configurable: true,
	value: function() {
		var o = this;

1kohei1

var a = {};
Object.defineProperty(a, 'a', {
	value: 1,
	writable: true,
	enumerable: true,
	configurable: true,
});
Object.defineProperty(a, 'b', {
	value: 2,
	writable: true,

1kohei1

var a = {
	a: 2,
};
("a" in a); // true
("b" in a); // false

a.hasOwnProperty("a"); // true
a.hasOwnProperty("b"); // false

// in operation also consults object prototype. So compare following two linces

1kohei1

var a = {
	get a() {
		return 2;
	}
}
Object.defineProperty(a, "b", {
	get: function() { return this.a * 2 },
	enumerable: true,
});
a.a; // 2