Adds an observer on a property.

This is the core method used to register an observer for a property.

Once you call this method, anytime the key's value is set, your observer will be notified. Note that the observers are triggered anytime the value is set, regardless of whether it has actually changed. Your observer should be prepared to handle that.

You can also pass an optional context parameter to this method. The context will be passed to your observer method whenever it is triggered. Note that if you add the same target/method pair on a key multiple times with different context parameters, your observer will only be called once with the last context you passed.

Observer Methods

Observer methods you pass should generally have the following signature if you do not pass a "context" parameter:

fooDidChange: function (sender, key, value, rev);

The sender is the object that changed. The key is the property that changes. The value property is currently reserved and unused. The rev is the last property revision of the object when it changed, which you can use to detect if the key value has really changed or not.

If you pass a "context" parameter, the context will be passed before the revision like so:

fooDidChange: function (sender, key, value, context, rev);

Usually you will not need the value, context or revision parameters at the end. In this case, it is common to write observer methods that take only a sender and key value as parameters or, if you aren't interested in any of these values, to write an observer that has no parameters at all.

Will add an observes handler to this object for a given property path.

In most cases, the path provided is relative to this object. However, if the path begins with a capital character then the path is considered relative to the window object.

Allows you to inspect a property for changes. Whenever the named property changes, a log will be printed to the console. This (along with removeProbe) are convenience methods meant for debugging purposes.

Notifies observers of all possible property changes.

Sometimes when you make a major update to your object, it is cheaper to simply notify all observers that their property might have changed than to figure out specifically which properties actually did change.

In those cases, you can simply call this method to notify all property observers immediately. Note that this ignores property groups.

Determines whether observers should be automatically notified of changes to a key.

If you are manually implementing change notifications for a property, you can override this method to return NO for properties you do not want the observing system to automatically notify for.

The default implementation always returns YES.

Begins a grouping of property changes.

You can use this method to group property changes so that notifications will not be sent until the changes are finished. If you plan to make a large number of changes to an object at one time, you should call this method at the beginning of the changes to suspend change notifications. When you are done making changes, call endPropertyChanges() to allow notification to resume.

Manually add a new binding to an object. This is the same as doing the more familiar propertyBinding: 'property.path' approach.

Decrements the value of a property.

This method will destroy the observable.

didChangeFor is a very important method which allows you to tell whether a property or properties have changed.

The key to using didChangeFor is to pass a unique string as the first argument, which signals, "Has anything changed since the last time this was called with this unique key?" The string can be anything you want, as long as it's unique and stays the same from call to call.

After the key argument, you can pass as many property arguments as you like; didChangeFor will only return true if any of those properties have changed since the last call.

For example, in your view's update method, you might want to gate DOM changes (generally a slow operation) on whether the root values have changed. You might ask the following:

if (this.didChangeFor('updateOnDisplayValue', 'displayValue')) {
  // Update the DOM.
}

In another method on the same view, you might send an event if that same value has changed:

if (this.didChangeFor('otherMethodDisplayValue', 'displayValue')) {
  // Send a statechart action.
}

Each call will correctly return whether the property has changed since the last time displayDidChange was called with that key. The following sequence of calls will return the following values:

• this.set('displayValue', 'value1');
• this.didChangeFor('updateOnDisplayValue', 'displayValue');

  true;

• this.didChangeFor('updateOnDisplayValue', 'displayValue'); false;
• this.didChangeFor('otherMethodDisplayValue', 'displayValue'); true;
• this.set('displayValue', 'value2');
• this.didChangeFor('updateOnDisplayValue', 'displayValue'); true;
• this.didChangeFor('updateOnDisplayValue', 'displayValue'); false;
• this.didChangeFor('updateOnDisplayValue', 'displayValue'); false;
• this.didChangeFor('otherMethodDisplayValue', 'displayValue'); false;

This method works by comparing property revision counts. Every time a property changes, an internal counter is incremented. When didChangeFor is invoked, the current revision count of the property is compared to the revision count from the last time this method was called.

Ends a grouping of property changes.

You can use this method to group property changes so that notifications will not be sent until the changes are finished. If you plan to make a large number of changes to an object at one time, you should call beginPropertyChanges() at the beginning of the changes to suspend change notifications. When you are done making changes, call this method to allow notification to resume.

Retrieves the value of key from the object.

This method is generally very similar to using object[key] or object.key, however it supports both computed properties and the unknownProperty handler.

Computed Properties

Computed properties are methods defined with the property() modifier declared at the end, such as:

fullName: function () {
    return this.getEach('firstName', 'lastName').compact().join(' ');
  }.property('firstName', 'lastName')

When you call get() on a computed property, the property function will be called and the return value will be returned instead of the function itself.

Unknown Properties

Likewise, if you try to call get() on a property whose values is undefined, the unknownProperty() method will be called on the object. If this method returns any value other than undefined, it will be returned instead. This allows you to implement "virtual" properties that are not defined upfront.

Convenience method to get an array of properties.

Pass in multiple property keys or an array of property keys. This method uses getPath() so you can also pass key paths.

Navigates the property path, returning the value at that point.

If any object in the path is undefined, returns undefined.

Returns YES if the object currently has observers registered for a particular key. You can use this method to potentially defer performing an expensive action until someone begins observing a particular property on the object.

Optionally, you may pass a target and method to check for the presence of a particular observer. You can use this to avoid creating duplicate observers in situations where that's likely.

Increments the value of a property.

This method will register any observers and computed properties saved on the object. Normally you do not need to call this method yourself. It is invoked automatically just before property notifications are sent and from the init() method of SC.Object. You may choose to call this from your own initialization method if you are using SC.Observable in a non-SC.Object-based object.

This method looks for several private variables, which you can setup, to initialize:

• _observers: this should contain an array of key names for observers you need to configure.

• _bindings: this should contain an array of key names that configure bindings.

• _properties: this should contain an array of key names for computed properties.

Logs the named properties to the console.

Convenience method to call propertyWillChange/propertyDidChange.

Sometimes you need to notify observers that a property has changed value without actually changing this value. In those cases, you can use this method as a convenience instead of calling propertyWillChange() and propertyDidChange().

Returns an array with all of the observers registered for the specified key. This is intended for debugging purposes only. You generally do not want to rely on this method for production code.

Notify the observer system that a property has just changed.

Sometimes you need to change a value directly or indirectly without actually calling get() or set() on it. In this case, you can use this method and propertyWillChange() instead. Calling these two methods together will notify all observers that the property has potentially changed value.

Note that you must always call propertyWillChange and propertyDidChange as a pair. If you do not, it may get the property change groups out of order and cause notifications to be delivered more often than you would like.

Notify the observer system that a property is about to change.

Sometimes you need to change a value directly or indirectly without actually calling get() or set() on it. In this case, you can use this method and propertyDidChange() instead. Calling these two methods together will notify all observers that the property has potentially changed value.

Note that you must always call propertyWillChange and propertyDidChange as a pair. If you do not, it may get the property change groups out of order and cause notifications to be delivered more often than you would like.

Use this to indicate that one key changes if other keys it depends on change. Pass the key that is dependent and additional keys it depends upon. You can either pass the additional keys inline as arguments or in a single array.

You generally do not call this method, but instead pass dependent keys to your property() method when you declare a computed property.

You can call this method during your init to register the keys that should trigger a change notification for your computed properties.

Remove an observer you have previously registered on this object. Pass the same key, target, and method you passed to addObserver() and your target will no longer receive notifications.

Will remove an observes handler from this object for a given property path.

In most cases, the path provided is relative to this object. However, if the path begins with a capital character then the path is considered relative to the window object.

Stops a running probe from observing changes to the observer.

Sets the key equal to value.

This method is generally very similar to calling object[key] = value or object.key = value, except that it provides support for computed properties, the unknownProperty() method and property observers.

Computed Properties

If you try to set a value on a key that has a computed property handler defined (see the get() method for an example), then set() will call that method, passing both the value and key instead of simply changing the value itself. This is useful for those times when you need to implement a property that is composed of one or more member properties.

Unknown Properties

If you try to set a value on a key that is undefined in the target object, then the unknownProperty() handler will be called instead. This gives you an opportunity to implement complex "virtual" properties that are not predefined on the object. If unknownProperty() returns undefined, then set() will simply set the value on the object.

Property Observers

In addition to changing the property, set() will also register a property change with the object. Unless you have placed this call inside of a beginPropertyChanges() and endPropertyChanges(), any "local" observers (i.e. observer methods declared on the same object), will be called immediately. Any "remote" observers (i.e. observer methods declared on another object) will be placed in a queue and called at a later time in a coalesced manner.

Chaining

In addition to property changes, set() returns the value of the object itself so you can do chaining like this:

record.set('firstName', 'Charles').set('lastName', 'Jolley');

Sets the property only if the passed value is different from the current value. Depending on how expensive a get() is on this property, this may be more efficient.

NOTE: By default, the set() method will not set the value unless it has changed. However, this check can skipped by setting .property().idempotent(NO) setIfChanged() may be useful in this case.

Navigates the property path, finally setting the value.

Navigates the property path, finally setting the value but only if the value does not match the current value. This will avoid sending unnecessary change notifications.

Inverts a property. Property should be a bool.

Called whenever you try to get or set an undefined property.

This is a generic property handler. If you define it, it will be called when the named property is not yet set in the object. The default does nothing.