Pro JavaScript for Web Apps pdf - EBook Free Download

CHAPTER 3 ADDING A VIEW MODELThe nice thing about this feature is that KO manages all of the dependencies, such that when mycomputed observable function relies on a regular observable data item, a change to the regular itemautomatically triggers an update in the computed value. I’ll use this behavior to manage the overall totallater in this chapter.Next, I need to add some elements with bindings to the template, as shown in Listing 3-8.Listing 3-8. Adding Elements to the Template to Support Subtotals $()($)The inner span element uses a text data binding to display the value of the subtotal property Icreated a moment ago. To make things more interesting, the outer span element uses another KObinding; this one is visible. For this binding, the child elements are hidden when the specified propertyis false-like (zero, null, undefined, or false). For truth-like values (1, true, or a non-null object or array),the child elements are displayed. I have specified the subtotal value for the visible binding, and thislittle trick means that I will display a subtotal only when the user enters a nonzero value into the inputelement. You can see the result in Figure 3-4.Figure 3-4. Selectively displaying subtotals65www.it-ebooks.info