title: KnockoutJS: Cannot read property 'fromJS' of undefined
body: <p>I use KnockoutJS in my app. Today I've got an error <code>Uncaught TypeError: Cannot read property 'fromJS' of undefined</code> in browser console and page doesn't load, although I'm loading Knockout plugin and recently everything worked fine.</p>
  
  <p>plugins from <code>head</code></p>
  
  <pre><code>&lt;script src="/assets/my/libs/knockout-2.1.0.js?body=1" type="text/javascript"&gt;&lt;/script&gt;
  &lt;script src="/assets/my/libs/knockout.mapping.js?body=1" type="text/javascript"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>my javascript file</p>
  
  <pre><code>var IllustratorModel = function (data) {
    var self = this;
    window.komodel = this;
    this.pre_offerings = ko.mapping.fromJS(data);
  
    ....
  </code></pre>
  
  <p>Thanks!</p>