Modal in javascript vanilla

gistfile1.js

//Based on http://jsfiddle.net/i_like_robots/W2DA8/

(function(name, context, definition) {
  if (typeof define === 'function' && define.amd) {
    define(definition);
  }
  else if (typeof module !== 'undefined' && module.exports) {
    module.exports = definition();
  }
  else {
    context[name] = definition();
  }
})('Modal', this, function() {

  var Modal = function(element) {
    this.target = element;

    if (!this.isOpen) {
      this._init();
    }
  };

  Modal.prototype._init = function() {
    var self = this;

    this.overlay = document.createElement('div');
    this.overlay.className = 'overlay_';
    this.overlay.style.position = 'fixed';
    this.overlay.style.top = 0;
    this.overlay.style.right = 0;
    this.overlay.style.bottom = 0;
    this.overlay.style.left = 0;
    this.overlay.style.zIndex = '99999';
    this.overlay.style.background = 'rgba(0, 0, 0, .5)';
    this.overlay.setAttribute('tabindex', -1);

    this.modalWindow = document.createElement('div');
    this.modalWindow.className = 'modal';
    this.modalWindow.style.position = 'fixed';
    this.modalWindow.style.top = 0;
    this.modalWindow.style.right = 0;
    this.modalWindow.style.bottom = 0;
    this.modalWindow.style.left = 0;
    this.modalWindow.style.width = '80%';
    this.modalWindow.style.height = '30%';
    this.modalWindow.style.margin = 'auto';
    this.modalWindow.style.background = '#EEE';
    this.modalWindow.style.zIndex = '99999';
    this.modalWindow.setAttribute('role', 'dialog');
    this.modalWindow.setAttribute('tabindex', 0);

    this.modalWrapper = document.createElement('div');
    this.modalWrapper.className = 'modal__wrapper';
    this.modalWrapper.style.overflow = 'auto';
    this.modalWrapper.style.height = '100%';

    this.modalContent = document.createElement('div');
    this.modalContent.className = 'modal__content';
    this.modalContent.style.padding = '1em';
    this.modalContent.style.textAlign = 'center';

    this.closeButton = document.createElement('button');
    this.closeButton.className = 'modal__close';
    this.closeButton.style.left = '10px';
    this.closeButton.style.top = '-45px';
    this.closeButton.style.position = 'relative';
    this.closeButton.innerHTML = 'Close';
    this.closeButton.setAttribute('type', 'button');

    this.closeButton.onclick = function() {
      self.close();
    };

    this.installButton = document.createElement('button');
    this.installButton.className = 'modal__install';
    this.installButton.style.left = '10px';
    this.installButton.style.top = '-45px';
    this.installButton.style.marginRight = '10px';
    this.installButton.style.position = 'relative';
    this.installButton.innerHTML = 'OK';
    this.installButton.setAttribute('type', 'button');

    this.installButton.onclick = function() {
      self.close();
    };

    this.modalWindow.appendChild(this.modalWrapper);
    this.modalWrapper.appendChild(this.modalContent);
    this.modalWindow.appendChild(this.installButton);
    this.modalWindow.appendChild(this.closeButton);

    this.isOpen = false;
  };

  Modal.prototype.open = function(text_modal, callback) {
    if (this.isOpen) {
      return;
    }

    this.modalContent.innerHTML = text_modal;

    this.target.appendChild(this.overlay);
    this.target.appendChild(this.modalWindow);
    this.modalWindow.focus();

    this.isOpen = true;

    if (callback) {
      callback.call(this);
    }
  };

  Modal.prototype.close = function(callback) {
    this.target.removeChild(this.modalWindow);
    this.target.removeChild(this.overlay);
    this.isOpen = false;

    if (callback) {
      callback.call(this);
    }
  };

  Modal.prototype.teardown = function() {
    if (this.isOpen) {
      this.close();
    }

    delete this.installButton;
    delete this.closeButton;
    delete this.modalContent;
    delete this.modalWrapper;
    delete this.modalWindow;
    delete this.overlay;
    delete this.isOpen;
  };

  return Modal;

});