var fc = {
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "name": "Location A"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [-75.343, 39.984]
      }
    }, {
      "type": "Feature",
      "properties": {
        "name": "Location B"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [-75.833, 39.284]
      }
    }, {
      "type": "Feature",
      "properties": {
        "name": "Location C"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [-75.534, 39.123]
      }
    }
  ]
};
 
var enveloped = turf.envelope(fc);
 
var resultFeatures = fc.features.concat(enveloped);
var result = {
  "type": "FeatureCollection",
  "features": resultFeatures
};
 
//=result