Example externs

Check the code folder.

I would advice to check the jQuery example, its without mentioning it that explicit there, also externs. The same mechanism that are describe here, are also at work there.

  • you need to "embed" the original js-files
  • you need to have externals
  • and that will enable you to write (very) similar Haxe code

I will give a short example of how to write, by hand, an extern. The example is from here)

The code used in this example can be found here.

How to start

Create a folder named foobar (please use a better name; any name will do) and create folders bin and src. See example below:

+ foobar
    + bin
    + src
        - Main.hx
    - build.hxml

if you have a JavaScript with looks like this


So copy and paste the code and save the file in the bin folder (!important)

// JavaScript
function MyJSClass() {
MyJSClass.SOME_PROP = 42;
MyJSClass.someFunc = function() {
    return "hello";
MyJSClass.prototype.myProp = null;
MyJSClass.prototype.myFunc = function(prop) {
    this.myProp = prop;


Create a file with the name MyJSClass.hx and save it in the src folder (!important)

Write your externs by hand like this:

// Haxe extern
extern class MyJSClass {
    static var SOME_PROP:Int;
    static function someFunc():String;

    var myProp:String;
    function new();
    function myFunc(prop:String):Void;

The Main.hx

Copy/paste the code and save it in the src folder.

package ;
class Main
    function new()
        trace("Externs Example");
        trace ("MyJSClass.SOME_PROP: " + MyJSClass.SOME_PROP); // 42 (Answer to The Ultimate Question of Life, the Universe, and Everything)
        trace ("MyJSClass.someFunc(): " + MyJSClass.someFunc()); // hello

        var _js = new MyJSClass();
        trace ("myProp: " + _js.myProp); // null
        _js.myFunc("Haxe Externs");
        trace ("myProp: " + _js.myProp); // Haxe Externs

    static public function main()
        var main = new Main();


Now we have to adjust the index.html

    <title>Haxe JS - Externs example</title></head>

<div class="container">Check your console.log</div>

<!-- the original javasript file -->
<script type="text/javascript" src="foobar.js"></script>

<!-- Your Haxe compiled script -->
<script type="text/javascript" src="example.js"></script>


The Haxe build file, build.hxml

There are a lot of different arguments that you are able to pass to the Haxe compiler. These arguments can also be placed into a text file of one per line with the extension hxml. This file can then be passed directly to the Haxe compiler as a build script.

# // build.hxml
-cp src
-main Main
-js bin/example.js
-dce full

Build js with Haxe

To finish and see what we have, build the file and see the result

  1. Open your terminal
  2. cd to the correct folder where you have saved the build.hxml
  3. type haxe build.hxml
  4. press enter

You could build everything directly in the terminal.

haxe -cp src -main Main -js bin/example.js -dce full

It will have the same result

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