change callback #5

Author: gerich-home

package.json

@@ -1,6 +1,6 @@
 {
   "name": "it-depends",
-  "version": "3.1.0",
+  "version": "3.2.0",
   "description": "Lightweight dependency tracking library for JavaScript",
   "files": [
     "src"

specs/generalChangeCallback.js

@@ -0,0 +1,120 @@
+var expect = require('chai').expect;
+var itDepends = require('../src/it-depends.js');
+
+describe('general change callback', function () {
+	var callCount;
+	var observableValue;
+	var subscription;
+	var lastChange;
+	
+	var expectLastChanges = function(expected) {
+		expect(lastChange.changed).to.equal(expected.changed);
+		expect(lastChange.from).to.equal(expected.from);
+		expect(lastChange.to).to.equal(expected.to);
+	};
+
+
+	beforeEach(function() {
+		callCount = 0;
+
+		observableValue = itDepends.value('Bob');
+
+		subscription = itDepends.onChange(function(changed, from, to) {
+			callCount++;
+			lastChange = { changed: changed, from: from, to: to };
+		});
+	});
+	
+	afterEach(function() {
+		subscription.disable();
+	});
+	
+	it('should not be triggered when new subscription is created', function () {
+		expect(callCount).to.equal(0);
+	});
+	
+	context('when when observable is changed', function() {
+		beforeEach(function() {
+			observableValue.write('Jack');
+		});
+
+		it('should be triggered once', function () {
+			expect(callCount).to.equal(1);
+			expectLastChanges({ changed: observableValue, from: 'Bob', to: 'Jack' });
+		});
+
+		it('should be triggered once when changed back', function () {
+			observableValue.write('Bob');
+			expect(callCount).to.equal(2);
+			expectLastChanges({ changed: observableValue, from: 'Jack', to: 'Bob' });
+		});
+	});
+	
+	context('when other observable value is created', function() {
+		var otherValue;
+		
+		beforeEach(function() {
+			otherValue = itDepends.value('Jack');
+		});
+		
+		it('should not be triggered when other observable is created', function () {
+			expect(callCount).to.equal(0);
+		});
+	
+		it('should be triggered once when observable is changed', function () {
+			observableValue.write('Jack');
+			
+			expect(callCount).to.equal(1);
+			expectLastChanges({ changed: observableValue, from: 'Bob', to: 'Jack' });
+		});
+	
+		it('should be triggered once when other observable is changed', function () {
+			otherValue.write('James');
+			
+			expect(callCount).to.equal(1);
+			expectLastChanges({ changed: otherValue, from: 'Jack', to: 'James' });
+		});
+	});
+	
+	context('when there is a computed depending on observable value', function() {
+		var computedValue;
+		
+		beforeEach(function() {
+			computedValue = itDepends.computed(function() {
+				return "Hello, " + observableValue();
+			});
+		});
+	
+		it('should be triggered once when observable is changed', function () {
+			observableValue.write('Jack');
+			
+			expect(callCount).to.equal(1);
+			expectLastChanges({ changed: observableValue, from: 'Bob', to: 'Jack' });
+		});
+	});
+	
+	context('when disabled', function() {
+		beforeEach(function() {
+			subscription.disable();
+		});
+	
+		it('should not be triggered when observable is changed', function () {
+			observableValue.write('Jack');
+			
+			expect(callCount).to.equal(0);
+		});
+
+		context('when enabled back', function() {
+			beforeEach(function() {
+				subscription.enable();
+			});
+		
+			it('should be triggered when observable is changed', function () {
+				observableValue.write('Jack');
+				
+				expect(callCount).to.equal(1);
+				expectLastChanges({ changed: observableValue, from: 'Bob', to: 'Jack' });
+			});
+		});
+	});
+});

specs/index.js

@@ -5,4 +5,5 @@ require('./computedWithComputedDependency.js');
 require('./unrelatedComputeds.js');
 require('./computedWith2ValueDependencies.js');
 require('./promiseValue.js');
-require('./parametricComputedWithNoDependencies.js');
+require('./parametricComputedWithNoDependencies.js');
+require('./generalChangeCallback.js');

src/it-depends.js

@@ -10,7 +10,9 @@
 
 var nop = function() {};
 var trackers = [nop];
+var handlers = {};
 var nextId = 0;
+var nextHandlerId = 0;
 var lastWriteVersion = 0;
 
 function notifyCurrentTracker(id, observableValue, currentValue) {
@@ -75,6 +77,22 @@ var computed = function(calculator) {
 };
 
 var library = {
+	onChange: function(handler) {
+		var handlerId = ++nextHandlerId;
+		
+		var subscription = {
+			enable: function() {
+				handlers[handlerId] = handler;
+			},
+			disable: function() {
+				delete handlers[handlerId];
+			}
+		};
+		
+		subscription.enable();
+		
+		return subscription;
+	},
 	value: function(initialValue) {
 		var currentValue = initialValue;
 		var id = ++nextId;
@@ -86,8 +104,16 @@ var library = {
 
 		self.write = function(newValue) {
 			if (currentValue !== newValue) {
+				var oldValue = currentValue;
 				currentValue = newValue;
 				lastWriteVersion++;
+				
+				for (var handlerId in handlers) {
+					if (!handlers.hasOwnProperty(handlerId))
+						continue;
+					
+					handlers[handlerId](self, oldValue, newValue);
+				}
 			}
 		};