Object.defineProperty

Object.defineProperty(obj, prop, descriptor)

// using __proto__
var obj = {};
var descriptor = Object.create(null // no inherited properties
// not enumerable, not configurable, not writable as defaults
descriptor.value = 'static';
Object.defineProperty(obj, 'key', descriptor

// being explicit
Object.defineProperty(obj, 'key', {
  enumerable: false,
  configurable: false,
  writable: false,
  value: 'static'
}

// recycling same object
function withValue(value) {
  var d = withValue.d || (
    withValue.d = {
      enumerable: false,
      writable: false,
      configurable: false,
      value: null
    }
  
  d.value = value;
  return d;
}
// ... and ...
Object.defineProperty(obj, 'key', withValue('static')

// if freeze is available, prevents adding or
// removing the object prototype properties
// (value, get, set, enumerable, writable, configurable)  
(Object.freeze || Object)(Object.prototype

var o = {}; // Creates a new object

// Example of an object property added
// with defineProperty with a data property descriptor
Object.defineProperty(o, 'a', {
  value: 37,
  writable: true,
  enumerable: true,
  configurable: true
}
// 'a' property exists in the o object and its value is 37

// Example of an object property added
// with defineProperty with an accessor property descriptor
var bValue = 38;
Object.defineProperty(o, 'b', {
  get: function() { return bValue; },
  set: function(newValue) { bValue = newValue; },
  enumerable: true,
  configurable: true
}
o.b; // 38
// 'b' property exists in the o object and its value is 38
// The value of o.b is now always identical to bValue,
// unless o.b is redefined

// You cannot try to mix both:
Object.defineProperty(o, 'conflict', {
  value: 0x9f91102,
  get: function() { return 0xdeadbeef; }
}
// throws a TypeError: value appears
// only in data descriptors,
// get appears only in accessor descriptors

var o = {}; // Creates a new object

Object.defineProperty(o, 'a', {
  value: 37,
  writable: false
}

console.log(o.a // logs 37
o.a = 25; // No error thrown
// (it would throw in strict mode,
// even if the value had been the same)
console.log(o.a // logs 37. The assignment didn't work.

var o = {};
Object.defineProperty(o, 'a', {
  value: 1,
  enumerable: true
}
Object.defineProperty(o, 'b', {
 value: 2,
 enumerable: false
}
Object.defineProperty(o, 'c', {
  value: 3
} // enumerable defaults to false
o.d = 4; // enumerable defaults to true
         // when creating a property by setting it

for (var i in o) {
  console.log(i
}
// logs 'a' and 'd' (in undefined order)

Object.keys(o // ['a', 'd']

o.propertyIsEnumerable('a' // true
o.propertyIsEnumerable('b' // false
o.propertyIsEnumerable('c' // false

var o = {};
Object.defineProperty(o, 'a', {
  get: function() { return 1; },
  configurable: false
}

Object.defineProperty(o, 'a', {
  configurable: true
} // throws a TypeError
Object.defineProperty(o, 'a', {
  enumerable: true
} // throws a TypeError
Object.defineProperty(o, 'a', {
  set: function() {}
} // throws a TypeError (set was undefined previously)
Object.defineProperty(o, 'a', {
  get: function() { return 1; }
} // throws a TypeError
// (even though the new get does exactly the same thing)
Object.defineProperty(o, 'a', {
  value: 12
} // throws a TypeError

console.log(o.a // logs 1
delete o.a; // Nothing happens
console.log(o.a // logs 1

var o = {};

o.a = 1;
// is equivalent to:
Object.defineProperty(o, 'a', {
  value: 1,
  writable: true,
  configurable: true,
  enumerable: true
}


// On the other hand,
Object.defineProperty(o, 'a', { value: 1 }
// is equivalent to:
Object.defineProperty(o, 'a', {
  value: 1,
  writable: false,
  configurable: false,
  enumerable: false
}

function Archiver() {
  var temperature = null;
  var archive = [];

  Object.defineProperty(this, 'temperature', {
    get: function() {
      console.log('get!'
      return temperature;
    },
    set: function(value) {
      temperature = value;
      archive.push{ val: temperature }
    }
  }

  this.getArchive = function() { return archive; };
}

var arc = new Archiver(
arc.temperature; // 'get!'
arc.temperature = 11;
arc.temperature = 13;
arc.getArchive( // [{ val: 11 }, { val: 13 }]

var pattern = {
    get: function () {
        return 'I always return this string, ' +
               'whatever you have assigned';
    },
    set: function () {
        this.myname = 'this is my name string';
    }
};


function TestDefineSetAndGet() {
    Object.defineProperty(this, 'myproperty', pattern
}


var instance = new TestDefineSetAndGet(
instance.myproperty = 'test';
console.log(instance.myproperty
// I always return this string, whatever you have assigned

console.log(instance.myname // this is my name string