title: JS errors when trying to use Laravel mix / webpack
body: <p>I have a webpack mix file, which looks like this.</p>
  
  <pre><code>let mix = require('laravel-mix');  
  let basePath = 'app/Resources/assets/sass/';  
  let jsPath = 'app/Resources/assets/js/';  
  mix.setPublicPath('./web');  
  mix.browserSync({proxy: 'rooms.test', ghost: false});
     .js('resources/js/app.js', 'public/js')
     .sass('resources/sass/app.scss', 'public/css')
  mix.sass(basePath + 'base.scss', 'web/assets_static/css');
  
  mix.combine(['./node_modules/imagesloaded/imagesloaded.pkgd.js',
      './node_modules/jquery/dist/jquery.js',
      './node_modules/slick-carousel/slick/slick.js',
      './node_modules/picturefill/picturefill.js',
      './node_modules/swipebox/src/js/jquery.swipebox.js',
      './node_modules/moment/min/moment.min.js',
      './node_modules/jquery-pjax/jquery.pjax.js',
      jsPath + '/info-pane.js',
      jsPath + '/base.js'], 'web/assets_static/js/base.js');
  </code></pre>
  
  <p>When I load the page, I get this error.</p>
  
  <pre><code>base.js:15708 Uncaught TypeError: Cannot read property 'defaults' of 
  undefined
  at HTMLDocument.&lt;anonymous&gt; (base.js:15708)
  at mightThrow (base.js:3583)
  at process (base.js:3651)
  </code></pre>
  
  <p>The line for this is :</p>
  
  <pre><code>$.pjax.defaults.timeout = 25000;
  </code></pre>
  
  <p>...so it appears that the base js file is for some reason not seeing the pjax file - even though it's in the webpack.mix.js.</p>
  
  <p>I'm tearing what little hair I have left out at this one - any help gratefully received. :-).</p>