title: Vis.js: Highlight selected node and grey out the others
body: <p>I am using vis.js and one of my tasks is to implement the following behavior: when I select a node, the node and its neighbors must be  highlighted. In the same time, all the other nodes must have a 'grayed-out' effect. 
  Looking at the vis.js showcase I saw this: <a href="https://kenedict.com/networks/startups/" rel="noreferrer">https://kenedict.com/networks/startups/</a> and it is exactly what I want to acquire. </p>
  
  <p>The question is...how do I achieve this effect easily? Do I really need to iterate between all the nodes in the graph and change their color properties?</p>
  
  <p>Thanks!</p>