Javascript. Simple Observer.

The task is to link 2 absolutely any objects. You cannot change the source code of objects.

Described below is designed for the reader's independence and the desire to understand the implementation.


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Example (exaggerated).

There are 2 objects in the house:

 <div id = "a1" onclick = "alert (123)"> </ div>
 <div id = "a2"> </ div>

And 1 javascript:

 Core = function () {
	 this.some = function (a, b, c, d, e, f, g) {
		 var a1 = $ ('a1'). innerHTML
		 var a2 = a + '' + b + '' + c + '' + d + '' + e + '' + f + '' + g
		 $ ('a1'). innerHTML = a1 + a2
	 }
	 this.another = function () {
		 var a = $ ('a1'). innerHTML
		 var a2 = 'some_text_more'
		 $ ('a1'). innerHTML = a + a2
	 }
	 this.another2 = function () {
		 var a = $ ('a2'). innerHTML
		 var a2 = 'yahoo'
		 $ ('a2'). innerHTML = a + a2
	 }
 }
 var Core = new Core ()

Required: Respond to a1.onclick by calling Core.another2

Implementation:

 var n = Observer.Attach ($ ('a1'), 'onclick', Core, 'another')

Remove Observer:

 Observer.Dettach ($ ('a1'), n)

Observer.
The implementation is built on the cloning method of the monitored object.
Observer.Attach clones the method, creating a new one with a unique name.
A new action is assigned to the monitored method, containing a clone call and a call to the necessary function (obj2.call_back)
The order of the call is controlled by the before parameter of the Observer.Attach method.

 Observer = function () {}
			
 Observer.prototype = {
	
	 List: {},
	
	 Attach: function (obj, method, obj2, call_back, before) {
		 var new_method = this.CloneOldMethod (obj, method)	
		 eval ('obj.' + method + '=' + this. NewDefaultMethod ('obj2', call_back, new_method, before))
		 return new_method 
	 },
	
	 Dettach: function (obj, observed_method) {
		 eval ('var m = this.List.' + observed_method)
		 eval ('obj.' + m.method + '= m.realization')
		 eval ('delete (obj.' + observed_method + ')')
		 eval ('delete (this.List.' + observed_method + ')')
	 },
	
	 NewDefaultMethod: function (obj_name, call_back, new_method, before) {
		 var m_old = 'this.' + new_method + '(arguments [0], arguments [1], arguments [2], arguments [3], arguments [4], arguments [5], arguments [6])'
		 var m_new = obj_name + '.' + call_back + '()'
		 var cmd = ''
		 cmd + = 'function () {'
		 before === true?  cmd + = m_new + ';' + m_old: cmd + = m_old + ';' + m_new
		 cmd + = '}'
		 return cmd
	 },
	
	 CloneOldMethod: function (obj, method) {
		 var new_method = 'a' + this.giveUnique ()
		 eval ('obj.' + new_method + '= obj.' + method)
		 eval ('this. List.' + new_method + '= {object: obj, \' method \ ': method, realization: obj.' + method + '}')
		 return new_method
	 },
	
	 giveUnique: function () {
		 return (new Date ()). getTime ()
	 }
 }

 Observer = new Observer ()