title: What are sub-modules in ES6?
body: <p>Suppose I have a ES6 module named <code>a.js</code>. <code>a.js</code> modules imports <code>b.js</code> and <code>c.js</code> modules. Similarly <code>b.js</code> imports <code>d.js</code> and <code>c.js</code> imports <code>e.js</code>.</p>
  
  <p>Now what I want to know is which ones are sub-modules and super-modules.</p>
  
  <p>I feel <code>b.js</code> and <code>c.js</code> are sub-modules of <code>a.js</code>. But I am not sure. Really confused. Please help.</p>
  
  <p>Thanks in advance.</p>