MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

• setProperty Updates a property value and notifies listeners if the value changed.
• updateProperty Like setProperty, but returns a promise that completes when all listeners have
been notified (the result in the promise is the new property value).
• getProperty Retrieves a property value as an observable object itself, which makes it possible
to bind within nested object structures (obj1.obj2.prop3, etc.).
• addProperty Adds a new property to the object that is automatically enabled for binding.
• removeProperty Removes a property altogether from the object.
Why would you want all of these? Well, there are some creative uses. You can call WinJS.-
Binding.bind, for example, directly on any observable source when you want to hook up another
function to a source property. This is like adding event listeners for source property changes, and you
can have as many listeners as you like. This is helpful for wiring up two-way binding, and it doesn’t in
any way have to be related to manipulating UI. The function just gets called on the property change.
This could be used to autosync a back-end service with the source object.
The Declarative binding sample also shows calling bind with an object as the second parameter, a
form that allows for binding to nested members of the source. The syntax looks like this:
bind(rootObject, { property: { sub-property: function(value) { ... } } })—whatever matches the
source object. With such an object in the second parameter, bind will make sure to invoke all the
functions assigned to the nested properties. In such a case, the return value of bind is an object with a
cancel method that will clear out this complex binding.
The notify method, for its part, is something you can call directly to trigger notifications. This is
useful with additional bindings that don’t necessarily depend on the values themselves, just the fact that
they changed. The major use case here is to implement computed properties—ones that change in
response to another property value changing.
WinJS.Binding also has some intelligent handling of multiple changes to the same source property.
After the initial binding, further change notifications are asynchronous and multiple pending changes to
the same property are coalesced. So, if in our example we made several changes to the name property
in quick succession:
login.name = "Kenichiro";
login.name = "Josh";
login.name = "Chris";
only one notification for the last value would be sent and that would be the value that shows up in
bound targets.
Finally, here are a few more functions hanging off WinJS.Binding:
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