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4.3.1.2 Building Interfaces Around Objects
A consequence of the previous section
is that users of GNU ease.js can continue to use strongly typed interfaces
even if the objects they are interfacing with do not support ease.js’
interfaces. Consider, for example, a system that uses XMLHttpRequest:
// modeled around XMLHttpRequest
var HttpRequest = Interface(
{
abort: [],
open: [ 'method', 'url', 'async', 'user', 'password' ],
send: [],
} );
var FooApi = Class(
{
__construct: function( httpreq )
{
if ( !( Class.isA( HttpRequest, httpreq ) ) )
{
throw TypeError( "Expecting HttpRequest" );
}
// ...
}
} );
FooApi( new XMLHttpRequest() ); // okay
Figure 4.6: Building an interface around needed functionality of XMLHttpRequest
This feature permits runtime polymorphism with preemptive failure instead of inconsistently requiring duck typing for external objects, but interfaces for objects handled through ease.js.