Really simple example of abstracts - creating an "extension" of AnchorElement with a custom constructor. Uses all inline code, and shows how implicit casts can be used when interacting with API that expects the underlying type.

AbstractExample.hx

// Compile with `haxe -js AbstractExample.js -dce full -main AbstractExample.hx`

import js.html.AnchorElement;

class AbstractExample {
	static function main() {
		var myAnchor = new MyAnchor( "http://google.com", "Click here!" );
		expectsAnchor( myAnchor ); // Notice how it automatically casts back down to AnchorElement
	}

	static function expectsAnchor( a:AnchorElement ) {
		trace ( a.href );
	}
}

abstract MyAnchor( AnchorElement ) from AnchorElement to AnchorElement {
	public inline function new( href:String, text:String ) {
		var doc = js.Browser.document;
		this = doc.createAnchorElement();
		this.href = href;
		this.innerHTML = text;
	}
}

AbstractExample.js

(function () { "use strict";
var AbstractExample = function() { }
AbstractExample.main = function() {
	var myAnchor;
	var this1;
	var doc = window.document;
	this1 = doc.createElement("a");
	this1.href = "http://google.com";
	this1.innerHTML = "Click here!";
	myAnchor = this1;
	AbstractExample.expectsAnchor(myAnchor);
}
AbstractExample.expectsAnchor = function(a) {
	console.log(a.href);
}
AbstractExample.main();
})();

I updated the code to use var doc = js.Browser.document, which gets rid of the "_this" reference and makes the generated code a little easier to understand...