The feature.id can only be set to number that worked

[wandergis]

I try to set feature.id by geojson-vt,but this library can only set type of number,but i can set grid_id which is string on mapbox-gl works well below:

source: {
  'grid': {
    type: 'vector',
    promoteId: 'grid_id',
    tiles: ['http://test.pbf']
  }
};