Ext often uses the concept of creating Config objects first, and instantiating them later. To be able to do so, a Config object must contain an property that indicates which class to instantiate (later). The three different special Ext properties available to specify the target class are:

That said, in ActionScript, you need not worry about all that. We introduced special semantics to ActionScript type casts when using them on object literals. (This is quite some cheating, too.) To create a Config object for a class MyClass , instead of calling its constructor, you type-cast an object code into that class:

var myClassConfig: MyClass = MyClass({
  id: "4711",  // inherited from Component._
  configOption1: "bar",  // MyClass Config property
  configOption2: 42  // the other MyClass Config property
});
  

This adds the appropriate xtype, alias , and/or xclass attributes.

However, in ActionScript, there is no way to type object literals. They are always of type Object and any properties are allowed. That's why you should use the following pattern to populate a Config object in ActionScript:

var myClassConfig = MyClass({});
myClassConfig.id = "4711";
myClassConfig.configOption1 = "bar";
myClassConfig.configOption2 = 42;

While this adds a bit more code, you now have type checks and gain IDE support like completion, documentation lookup and navigation.

If needed, you can then use different ways to instantiate the corresponding class:

var myClassInstance: MyClass = new MyClass(myClassConfig);
// OR
var myClassInstance: MyClass = Ext.create(myClassConfig); // careful: no type check!
// OR
var myClassInstance: MyClass = MyClass(Ext.create(myClassConfig)); // at least a run-time type check