observingproxy

Observing proxy

A proxy for observing object state changes.

This module is based on the Object.defineProperty method and serves as an interface to the user provided object, notifying subscribers about the user object changes.

var obj={person:'Eddie',age:22};

_o.onUpdate(obj,{
  age:function(value){
    if(value>this.oldValue)
      console.log('Happy birthday, Peter!')
  },
  person:function(value){
    console.log(this.oldValue+' is now '+value);
  }
});

_o(obj).person='Peter';
//> Eddie is now Peter
_o(obj).age++;
//> Happy birthday, Peter!

Install

npm install observingproxy

or

bower install observingproxy

Advanced usage (implemented with Object.observe in mind)

var obj={person:'Peter',age:22};

_o.observe(obj,function(changes){
  for(var i=0;i<changes.length;i++)
    if(changes[i].name==='age')
      if(changes[i].object.age>changes[i].oldValue)
        console.log('Happy birthday, Peter!')
});

_o(obj).age++;
//> Happy birthday, Peter!

Note: it works only with property update. add or delete operations are not supported.

With arrays

var arr=[1,2,3];

_o.observe(arr,function(changes){
  for(var i=0;i<changes.length;i++)
    if(changes[i].type==='splice')
      console.log('Array changed')
});

_o(arr).push(4);
//> Array changed

Error handling and destructor

var observer=_o.onUpdate(null,'name',function(value){
  //...
});

// Throw observation exception here
try{
  observer.report();
}
catch(e){throw e}
// Observing proxy error: target is null

// Destroy your observer
observer.destroy();

Deferred observer notification

While proxy applies property modification immediately, it sends the observer notification call to the end of execution thread using setTimeout method as a wrapper.

So now, if you do

_o.observe(obj,function(changes){
  // iterate changes
});

_o(obj).p1=1;
_o(obj).p2=2;
_o(obj).p3=3;

observer is notified only once with changes argument containing latest modifications. It makes observer a load sustainable to an observed object being intensively modified.