02-objects.md

Basic concepts

• An object is a compsite value: it aggregates multiple values and allows you to store and retrieve those valaues by name.
• Object is like hashtable, dictionary, associcative arrary
• Any value in JS that is NOT a string, a number, a boolean, null or undefined is an object
• A property has a name and a value. A property name may be anything, including empty string. The value of a property is called property attribute.
• The property name of an object must be unique.

Object creation

• create via object literals:

  var empty = {};
  var point = {x: 0, y: 0};
  var contact = {'first name': 'James', 'last name': 'Bond', 'age': 30, 'nationality': 'British'};

• create with new

  var o = new Object();
  var a = new Arrary();
  var d = new Date();
  var r = new RegExp('js');

• Object.create()

var o1 = Object.create({x: 1, y: 1});
var o2 = Object.create(null);  // inherits no props or methods
var o3 = Object.create(Object.prototype); // like {} or new Object(), it's an empty object

Object and Instances

funciton Person(first, last) {
  this.first = first;
  this.last = last;
}

Person.prototype.fullName = function() {
  return this.first + ' ' + this.last;
}

p = new Person('Steve', 'Jobs');
console.log(p.fullName()); // Steve Jobs
console.log(typeof Person); // function
console.log(typeof p); // object
console.log(p instanceof Person); true
console.log(p.constructor.name); // Person
console.log(Person.name); // Person