title: What is process.env.BASE_URL in vue js?
body: <p>When I manually selected presets when installing vue using vue cli. I stumbled upon process.env.BASE_URL. I was tryng to find it in the internet but to no avail, I can't find any decent explanation.
  Here's the code.</p>
  
  <pre><code>const router = new VueRouter({
    mode: 'history',
    base: process.env.BASE_URL,
    routes
  })
  </code></pre>