title: d3js v5 + Topojson v3 Optimization about joining csv & json
body: <p>In order to make maps, I need to import some values from csv to json <strong>directly in the code</strong>.
  For loading json and csv files, I use an asynchronous operation with Promise object and I use two loops and a common key to add new properties on json file.</p>
  
  <pre><code>for (var i=0; i&lt; fr[1].length;i++){
          var csvId = fr[1][i].codgeo;
          var csvValue1 = parseFloat(fr[1][i].value1);
          var csvValue0 = parseFloat(fr[1][i].value0);
          for (var j=0; j&lt;topojson.feature(fr[0],fr[0].objects.dep_GEN_WGS84_UTF8).features.length;j++){
            var jsonId = topojson.feature(fr[0],fr[0].objects.dep_GEN_WGS84_UTF8).features[j].properties.codgeo;
            if (csvId === jsonId) {
              topojson.feature(fr[0],fr[0].objects.dep_GEN_WGS84_UTF8).features[j].properties.value1 = csvValue1;
              topojson.feature(fr[0],fr[0].objects.dep_GEN_WGS84_UTF8).features[j].properties.value0 = csvValue0;
              break;
  </code></pre>
  
  <p>Everything is working but show up the map on the web takes time.
  Is there a way to optimize the loading time of the map ?</p>
  
  <p>Here is a sample of my code : <a href="https://plnkr.co/edit/ccwIQzlefAbd53qnjCX9?p=preview" rel="nofollow noreferrer">https://plnkr.co/edit/ccwIQzlefAbd53qnjCX9?p=preview</a></p>