KVC and KVO from a Javascript standpoint

Coming from Javascript, Key Value Coding (KVC) and Key Value Observing (KVO) will seem pretty familiar. KVC lets you handle your object just like a hash (NSDictionary in Cocoa terms), KVO sends a notification when a dictionary key has been changed.
Key Value Coding
// Read a value

// Set a value
myObject['myValue'] = 123
// Read a value
[myObject valueForKey:@"myValue"]

// Set a value 
[myObject setValue:[NSNumber numberWithInt:123] forKey:@"myValue"]
Key Value Observing
function callMeWhenMyValueChanged(newValue)
   // Receiving the new value of myObject.myValue

// Setup a notification for when myObject.myValue changes
myObject.__defineSetter__('myValue', callMeWhenMyValueChanged)

// Set a value 
myObject['myValue'] = 123
// Add an observer for myObject's myValue
[myObject addObserver:myObserverObject  

// Set a value
[myObject setValue:[NSNumber numberWithInt:123] forKey:@"myValue"]

// When setting the new value, KVO calls myObserver's 
// observeValueForKeyPath:ofObject:change:context:

Note the differences : in Javascript, a setter can be any function, even a global one. In ObjC, an observer function must be member of a class. In Javascript, you define the name of your function. In ObjC, the KVO notification has a fixed name (observeValueForKeyPath:ofObject:change:context) — it's called a protocol, and it's the subject of the next post : ObjC protocols from a Javascript standpoint.

Objective-C from Javascript

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