title: laravel 'Undefined index:' when mixing a js file
body: <p>I am trying to figure out laravel for a small project I am working on. </p>
  
  <p>I want to load a js file on a particular view(not the entire app) so I have created a <code>client.js</code> file in <code>resources/assets/js</code></p>
  
  <p>In the view --</p>
  
  <p><code>&lt;script src="{{ mix('js/client.js') }}"&gt;&lt;/script&gt;</code></p>
  
  <p>in webpack.mix.js</p>
  
  <p><code>mix.js('resources/assets/js/app.js', 'public/js', 'resources/assets/js/client.js')</code></p>
  
  <p>And run <code>npm run dev</code> which doesn't return any errors. </p>
  
  <p>However when I try to load the view in question I get the error --</p>
  
  <p><code>Undefined index: /js/client.js (View: /var/www/resources/views/devices/search.blade.php)</code></p>
  
  <p>What am I doing wrong/ missing?</p>