solution - super() not calling parent's constructor on IE9 - https://github.com/babel/babelify/issues/133

README.md

babel/babelify#133

For super calls to work in IE9, you must enable "loose" mode for the class transform. For inherited static properties to work in IE9, you must also add the babel-plugin-transform-proto-to-assign plugin.

build.js

var fs = require('fs');
var browserify = require('browserify');

browserify('./index.js')
  .transform('babelify', {
    plugins: [
      'transform-es2015-block-scoping',
      ['transform-es2015-classes', {loose: true}],
      'transform-proto-to-assign',
    ],
  })
  .bundle()
  .pipe(fs.createWriteStream('./out.js'));

index.js

class test {
  constructor() {
    console.log('test');
  }
}

class test2 extends test {
  constructor() {
    super();
    console.log('test2');
  }
}

new test2();

out.js

(function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){
function _defaults(obj, defaults) { var keys = Object.getOwnPropertyNames(defaults); for (var i = 0; i < keys.length; i++) { var key = keys[i]; var value = Object.getOwnPropertyDescriptor(defaults, key); if (value && value.configurable && obj[key] === undefined) { Object.defineProperty(obj, key, value); } } return obj; }

function _possibleConstructorReturn(self, call) { if (!self) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return call && (typeof call === "object" || typeof call === "function") ? call : self; }

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function, not " + typeof superClass); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, enumerable: false, writable: true, configurable: true } }); if (superClass) Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : _defaults(subClass, superClass); }

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

var test = function test() {
  _classCallCheck(this, test);

  console.log('test');
};

var test2 = function (_test) {
  _inherits(test2, _test);

  function test2() {
    _classCallCheck(this, test2);

    var _this = _possibleConstructorReturn(this, _test.call(this));

    console.log('test2');
    return _this;
  }

  return test2;
}(test);

new test2();

},{}]},{},[1]);

package.json

{
  "name": "ie9-class-inherit-super-demo",
  "version": "0.0.0",
  "description": "https://github.com/babel/babelify/issues/133",
  "scripts": {
    "build": "node build.js",
    "test": "node out.js"
  },
  "author": "Andres Suarez <zertosh@gmail.com>",
  "license": "MIT",
  "dependencies": {
    "babel": "^6.3.26",
    "babel-plugin-transform-es2015-block-scoping": "^6.4.0",
    "babel-plugin-transform-es2015-classes": "^6.4.0",
    "babel-plugin-transform-proto-to-assign": "^6.4.0",
    "babelify": "^7.2.0",
    "browserify": "^13.0.0"
  }
}

You're a life saver. Took me forever to hunt down this bug -- this solution worked for me.