async-watch

async-watch

AsyncWatch is a small library for watching javascript/node.js objects. It uses Object.defineProperty which makes it compatible with most browsers. Any changes happening within present tick will be called on the next available one.

Features

• Asynchronous execution (Changes are triggered on requestAnimationFrame in browser and on process.nextTick in Node)
• Being Asynchronous means we don’t have to worry about the execution flow, details below
• Works in Node and Browser
• No Dirty Checking or Object.observe
• Using Object.defineProperty() makes it compatible with all modern browser down to IE 9
• Order of watchers is preserved
• Deep watch properties
• Ability to inspect change type for Arrays (init,splice, push)
• Computed Properties
• Get old and new values in the change callback
• Can watch any type of Object for example Watching DOM Node properties and attributes
• Restoring watchers after objects are destroyed
• Can be used as the back-bone to create a custom efficient two-way binding system
• Comprehensive test coverage

Install

npm install async-watch --save

Examples

var AsyncWatch = require('async-watch').AsyncWatch;
var obj = {}; // creating an empty object
AsyncWatch(obj, 'a.b.c', function(value){
    console.log('set', value);
});
// You can pass an array as well
//AsyncWatch(obj, ['a', 'b', 'c'])

As you can see here, we start with an empty object. AsyncWatch will set a watcher on property "a", which knows about its descendands

 obj.a = {
  b : {
   c : 1
  }
 };
 obj.a.b.c = 2;
 obj.a.b.c = 3;
 setTimeout(function(){
    obj.a.b.c = 4;
 },0)

The output will look like this:

set 3
set 4

Callback is called on "transaction commit". Each transaction is a requestAnimationFrame tick. Surely, initial transaction loop happens when first value is changed.

Worth mentioning: Transactions happen on demand, without "perpetual" loop or/and any other dirty checkers.

Destroying a watcher

Destroys a watcher (does not destroy its descendants or similar watchers)

var watcher = AsyncWatch(obj, 'a', function(value) {
});
watcher.destroy();

Watching many objects

watchAll is not implemented yet, however subscriptions are introduced. Each watcher returns a "transaction" / watcher.

var obj = {
  a : 1,
  b : 2
}
var watcher1 = AsyncWatch(obj, 'a', function(value) {
});
var watcher2 = AsyncWatch(obj, 'b', function(value) {
});

var subscription = AsyncWatch.subscribe([watcher1, watcher2], function(changes){
   console.log(changes)
})

Subscribers' callback guarantees all watchers to be in sync.

Outputs:

{a : 1, b: 2 }

Unfortunately, subscriptions won't clean up themselves, you need to do it manually.

subscription.unsubscribe();

If you want to unsubscribe and destroy corresponding watchers:

subscription.destroy();

Computed properties

You can define a computed property.

var obj = {
   firstName : "Bob",
   lastName : "Marley"
}

AsyncComputed(obj, 'fullName', ['firstName', 'lastName'],
	self =>`Name is ${self.firstName} ${self.lastName}`);


obj.lastName = "Foo";
obj.lastName = "Foo1";
AsyncWatch(obj, 'fullName', (value) => {
   // Name is Bob Foo1
});

Watching arrays

var obj = {
   users : [{name : "John"}, {name : "Bob"}]
}


AsyncWatchArray(obj, 'users', function(array,events){
   console.log(events);
});

Triggers events: "init" "push" "splice"

To have better understanding check these test/sync_test.js

Contribution

Contribution is greatly appreciated! Please, run tests before submitting a pull request.