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JavaScript Events and Client-side ViewModel

Every DotVVM page includes Dotvvm.js which defines dotvvm in the global scope. This object can be used to access viewmodel and react to various page events.

Accessing the viewmodel

DotVVM stores the page viewmodel in dotvvm.viewModels.root.viewModel object. The viewmodel corresponds with the C# class, and all properties and array elements are wrapped in Knockout observables.

To read data from the viewmodel, you need to evaluate every observable in the property path:

// C# - server-side expression
this.EventAttendees[2].FirstName

// JavaScript - client-side expression
dotvvm.viewModels.root.viewModel.EventAttendees()[2]().FirstName()

To set data, you need to call the observable and pass the new value as an argument:

// C# - server-side expression
this.EventAttendees[2].FirstName = "test";

// JavaScript - client-side expression
dotvvm.viewModels.root.viewModel.EventAttendees()[2]().FirstName("test");

Working with dates

DotVVM uses special handling for Date values in JavaScript. To prevent automatic conversions to local time on the client side, DotVVM stores date & time values as strings in the following format: yyyy-MM-ddTHH:mm:ss.fffffff

To convert JavaScript Date into DotVVM representation, use the following function:

dotvvm.serialization.serializeDate(date, convertToUtc);

To convert DotVVM date representation to JavaScript Date, use the following function:

dotvvm.globalize.parseDotvvmDate(date);

Reacting to DotVVM events

DotVVM publishes the following events:

  • init - occurs as soon as the page and DotVVM scripts is loaded and the viewmodel is applied to the page DOM
  • beforePostback - occurs before every postback
  • afterPostback - occurs after a postback is completed successfully
  • error - occurs when a postback fails with an error
  • spaNavigating - occurs before navigation to a new page in SPA mode
  • spaNavigated - occurs after navigated to a new page in SPA mode
  • redirect - occurs when a postback results in a redirect to a new page

DotVVM 2.0 introduces new events for postback handlers, static commands and other situations (like postback rejection).

DotVVM events contain subscribe and unsubscribe methods:

var handler = function (args) {
    // handler code
};

dotvvm.events.beforePostback.subscribe(handler);
dotvvm.events.beforePostback.unsubscribe(handler);

The init event has a special behavior - when you subscribe to it after the event occured, the handler will be invoked immediately.

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