Description of how JavaScript objects work

JavaScript Objects

Objects have four states:
	properties can be	added | deleted | modified* 	| do it with		| check with
	Default 		√	  | √	    | √		| n/a 			| n/a
	preventExtensions	X	  | √	    | √	  	| preventExtensions	| isExtensible
	seal			X	  | X	    | √		| seal			| isSealed
	freeze			X	  | X	    | X		| freeze		| isFrozen

* by changing any of the four attributes below

You can make an object in three different ways:
new Object(), Object.create(), or using the literal notation (initializer notation)

Properties come in two flavors:
I. Data properties
II. Accessor properties

Data properties have four attributes:
1. value	
	The property's value.

2. writable	
	true or false. Whether the property's value can be written to. (For example, o["p"] = 1)

3. enumerable	
	true or false. Whether the property shows in some loop constructs, such as for (var x in o) {…} and  Object.keys(o).

4. configurable	
	true or false. Whether the property can be deleted (For example, delete o["p"]) and whether its attributes can be changed.

Accessor properties have the same writeable and configurable attributes as data properties, but in addition (respectively):

5. get

6. set

Properties an be created with:
Object.defineProperty(obj, 'propName', { value, writable, enumerable, configurable });

Defaults given an empty object are:
{ value: undefined, writable: false, enumerable: false, configurable: false }

However, creating a new property by assigning to it uses defaults: 
{ value: "your value", writable: true, enumerable: true, configurable: true }

Property attributes can be accessed with: 
Object.getOwnPropertyDescriptor(obj) or
Object.getOwnPropertyDescriptor(obj, "propName") or
Reflect.getOwnPropertyDescriptor(obj, "propName")