Example extern class taking from our own LunaTea development code.

ExternExample.hx

package;

//Expose metatag is used to make sure that when the code is being referenced in the target language it'll be exposed
//for user's to override. I use this in JS to allow for modification, which is core to RPGMakerMV/MZ.
//Native metatag is used to make sure that when the code is compiled it uses the proper name.
//Native works both on classes and fields, which you can see for the x, y fields below.
@:expose("Point")
@:native("Point")
extern class Point extends pixi.core.math.Point {
 /**
  * The point class.
  *
  * @class Point
  * @constructor
  * @param {Number} x The x coordinate
  * @param {Number} y The y coordinate
  */
 public function new(?x: Float, ?y: Float);

 /**
  * The x coordinate.
  *
  * @property x
  * @type Number
  */
 @:native("x")
 public var _x: Float;

 /**
  * The y coordinate.
  *
  * @property y
  * @type Number
  */
 @:native("y")
 public var _y: Float;
}