mapbox-gl.js drag a point and have a line that connects it to another point move by mpmckenna8

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8' />
<title>Create a draggable point</title>
<meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
<script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.53.0/mapbox-gl.js'></script>
<link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.53.0/mapbox-gl.css' rel='stylesheet' />
<style>
body { margin:0; padding:0; }
#map { position:absolute; top:0; bottom:0; width:100%; }
</style>
</head>
<body>
 
 
<style>
.coordinates {
background: rgba(0,0,0,0.5);
color: #fff;
position: absolute;
bottom: 10px;
left: 10px;
padding:5px 10px;
margin: 0;
font-size: 11px;
line-height: 18px;
border-radius: 3px;
display: none;
}
</style>
 
<div id='map'></div>
<pre id='coordinates' class='coordinates'></pre>
 
<script src='./map.js'>

</script>
 
</body>
</html>

map.js

mapboxgl.accessToken = 'pk.eyJ1IjoibXBtY2tlbm5hOCIsImEiOiJfYWx3RlJZIn0.v-vrWv_t1ytntvWpeePhgQ';
var coordinates = document.getElementById('coordinates');
var map = new mapboxgl.Map({
  container: 'map',
  style: 'mapbox://styles/mapbox/streets-v9',
  center: [0, 0],
  zoom: 2
  });
 
var canvas = map.getCanvasContainer();


var geojson = {
  "type": "FeatureCollection",
  "features": [{
    "type": "Feature",
    "geometry": {
      "type": "Point",
      "coordinates": [0, 0]
    }
  }]
};

var parent = {
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [13, 4]
}
}]
};


var liner = {
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "LineString",
"coordinates": [
  parent.features[0].geometry.coordinates, geojson.features[0].geometry.coordinates
]
}
}]
};
 
function onMove(e) {
  var coords = e.lngLat;
   
  // Set a UI indicator for dragging.
  canvas.style.cursor = 'grabbing';
   
  // Update the Point feature in `geojson` coordinates
  // and call setData to the source layer `point` on it.
  geojson.features[0].geometry.coordinates = [coords.lng, coords.lat];
  liner.features[0].geometry.coordinates[1] = [coords.lng, coords.lat];

  map.getSource('point').setData(geojson);
  map.getSource('liner').setData(liner);

}
 
function onUp(e) {
  var coords = e.lngLat;
   
  // Print the coordinates of where the point had
  // finished being dragged to on the map.
  coordinates.style.display = 'block';
  coordinates.innerHTML = 'Longitude: ' + coords.lng + '<br />Latitude: ' + coords.lat;
  canvas.style.cursor = '';
   
  // Unbind mouse/touch events
  map.off('mousemove', onMove);
  map.off('touchmove', onMove);
}
 
map.on('load', function() {
   
  // Add a single point to the map
  map.addSource('point', {
    "type": "geojson",
    "data": geojson
  });

  map.addSource('parent', {
    "type": "geojson",
    "data": parent
  });
   
  map.addLayer({
    "id": "point",
    "type": "circle",
    "source": "point",
    "paint": {
      "circle-radius": 10,
      "circle-color": "#3887be"
    }
  });

  map.addLayer({
    "id": "parent",
    "type": "circle",
    "source": "parent",
    "paint": {
      "circle-radius": 30,
      "circle-color": "#e887be"
    }
  });

map.addLayer({
  'id': 'liner',
  'type': 'line',
  'source': {
  'type': 'geojson',
  'data': liner
  },
  'layout': {
    'line-cap': 'round',
    'line-join': 'round'
  },
  'paint': {
    'line-color': '#ed6498',
    'line-width': 5,
    'line-opacity': .8
  }
});


 
// When the cursor enters a feature in the point layer, prepare for dragging.
map.on('mouseenter', 'point', function() {
  map.setPaintProperty('point', 'circle-color', '#3bb2d0');
  canvas.style.cursor = 'move';
});
 
map.on('mouseleave', 'point', function() {
  map.setPaintProperty('point', 'circle-color', '#3887be');
  canvas.style.cursor = '';
});
 
map.on('mousedown', 'point', function(e) {
  // Prevent the default map drag behavior.
  e.preventDefault();
   
  canvas.style.cursor = 'grab';
   
  map.on('mousemove', onMove);
  map.once('mouseup', onUp);
});
 
  map.on('touchstart', 'point', function(e) {
    if (e.points.length !== 1) return;
     
    // Prevent the default map drag behavior.
    e.preventDefault();
     
    map.on('touchmove', onMove);
    map.once('touchend', onUp);
  });
});