title: cytoscape js, how define node with background-image from a json data file
body: <p>I want use cytoscape librairy for build a sample graphs but I want display on each node different images. </p>
  
  <p>I tried that : </p>
  
  <pre><code>[ 
    {
      "data": [
        "id0"
      ],
      "position": {
        "x": 44,
        "y": 93
      }
    },
    {
      "data": [
        "id1"
      ],
      "position": {
        "x": 77,
        "y": 200
      },
      "background-image": [
        "https://upload.wikimedia.org/wikipedia/commons/b/b4/High_above_the_Cloud_the_Sun_Stays_the_Same.jpg",
        "https://upload.wikimedia.org/wikipedia/commons/thumb/f/fc/Pigeon_silhouette_4874.svg/1000px-Pigeon_silhouette_4874.svg.png"
      ],
      "background-fit": "cover cover",
      "background-image-opacity": 0.5
    }
  ]
  </code></pre>
  
  <p>But when I load my page I see two 'empty' nodes. I used this javascript script : </p>
  
  <pre><code>fetch('data.json', {mode: 'no-cors'})
    .then(function(res) {
      return res.json()
    })
    .then(function(data) {
      var cy = window.cy = cytoscape({
        container: document.getElementById('cy'),
  
        layout: {
          name: 'preset',
        },
  
        style: [
          {
            selector: 'node',
            style: {
              'height': 20,
              'width': 20,
            }
          }
        ],
  
        elements: data
      });
    }); 
  </code></pre>
  
  <p>Where is my mistake ? How can I generate a graph with different background images on each nodes ? </p>
  
  <p>Thanks you :) </p>