Angular 2 type annotation with babel (babel --experimental with experimental branch)

1_before.js

class HelloComponent {
  constructor(foo: Foo, bar: Bar) { }
}

2_after.js

"use strict";

var _classCallCheck = function (instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } };

var HelloComponent = function HelloComponent(foo, bar) {
  _classCallCheck(this, HelloComponent);
};

HelloComponent.parameters = [[Foo], [Bar]];

type-annotation.js

var babel = require('./babel/lib/babel/api/node');

(function () {
  var t = require('./babel/lib/babel/types');
  var File = require('./babel/lib/babel/transformation/file');
  var Transformer = require('./babel/lib/babel/transformation/transformer');

  var key = 'angular2.typeAnnotation';
  var rawTransformer = {
    check: t.isClass,
    ClassDeclaration: function ClassDeclaration(node, parent, scope, file) {
      var classRef = node.id;
      var className = classRef.name;
      var classBody = node.body.body;
      var annotations = [];
      classBody.forEach(function (bodyNode) {
        if (bodyNode.type === 'MethodDefinition' && bodyNode.kind === 'constructor') {
          var params = bodyNode.value.params;
          params.forEach(function (param) {
            var annotation = param.typeAnnotation && param.typeAnnotation.typeAnnotation.id.name;
            annotations.push(annotation);
          });
        }
      });
      var params = t.arrayExpression(annotations.map(function (annotation) {
        return t.arrayExpression([t.identifier(annotation)]);
      }));
      var propertyName = t.memberExpression(classRef, t.identifier('parameters'), false);
      var assignment = t.expressionStatement(t.assignmentExpression('=', propertyName, params));
      return [node, assignment];
    }
  };
  var transformer = new Transformer(key, rawTransformer, {});

  File.prototype.buildPlugins = function buildPlugins(stack) {
    var pass = transformer.buildPass(this);
    stack.push(pass);
  };
})();

var code = [
  'class HelloComponent {',
  '  constructor(foo: Foo, bar: Bar) { }',
  '}'
].join('\n');
var result = babel.transform(code);

console.log('--- Before ---');
console.log(code);
console.log('--- After ---');
console.log(result.code);