title: How to use the :not selector in Cytoscape.js? (To select nodes that don't have an attribute)
body: <p>I'm trying to use the <strong>:not</strong> selector in cytoscape.js. I want to select all nodes that don't have a specific attribute to open an context menu. E.g.:</p>
  
  <pre><code>cy.cxtmenu({
      selector: not('node.selection'),
      commands: [ .... ]
  });
  </code></pre>
  
  <p>But I'm not sure how I can do this in cytoscape.js. Any help will be welcome.</p>