JsAction

JsAction is a tiny event delegation library that allows decoupling the DOM nodes on which the action occurs from the JavaScript code that handles the action.

The traditional way of adding an event handler is to obtain a reference to the node and add the event handler to it. JsAction allows us to map between events and names of handlers for these events via a custom HTML attribute called jsaction.

Separately, JavaScript code registers event handlers with given names which need not be exposed globally. When an event occurs the name of the action is mapped to the corresponding handler which is executed.

Finally, JsAction uncouples event handling from actual implementations. Thus one may late load the implementations, while the app is always able to respond to user actions marked up through JsAction. This can help in greatly reducing page load time, in particular for server side rendered apps.

Building

JsAction is built using the Closure Compiler. You can obtain a recent compiler from the site.

JsAction depends on the Closure Library. You can obtain a copy of the library from the GitHub repository.

The compiler is able to handle dependency ordering automatically with the --only_closure_dependencies flag. It needs to be provided with the sources and any entry points.

See the files dispatch_auto.js, eventcontract_auto.js, and eventcontract_example.js for typical entry points.

Here is a typical command line for building JsAction's dispatch_auto.js:

find path/to/closure-library path/to/jsaction -name "*.js" |
    xargs java -jar compiler.jar  \
    --output_wrapper="(function(){%output%})();" \
    --only_closure_dependencies \
    --closure_entry_point=jsaction.dispatcherAuto

Usage

In the DOM

Actions are indicated with the jsaction attribute. They are separated by ;, where each one takes the form:

[eventType:]<namespace>.<actionName>

If an eventType is not specified, JsAction will assume click.

<div id="foo"
     jsaction="leftNav.clickAction;dblclick:leftNav.doubleClickAction">
  some content here
</div>

In JavaScript

Set up

var eventContract = new jsaction.EventContract;

// Register the event types we care about.
eventContract.addEvent('click');
eventContract.addEvent('dblclick');

var dispatcher = new jsaction.Dispatcher;

eventContract.dispatchTo(goog.bind(dispatcher.dispatch, dispatcher));

Register individual handlers

/**
 * Do stuff when actions happen.
 * @param {!jsaction.ActionFlow} flow Contains the data related to the action
 *     and more. See actionflow.js.
 *
 */
myapp.LeftNav.prototype.doStuff = function(flow) {
  // do stuff
};

myapp.LeftNav.prototype.registerHandlers = function() {
  dispatcher.registerHandlers(
      'leftNav',                       // the namespace
      this,                            // handler object
      {                                // action map
        'clickAction' : this.doStuff,
        'doubleClickAction' : this.doStuff
      });
};