Color layers by aggregation

[mikefab]

8 lines of code by @carloscdias

    let matches = document.querySelectorAll("input[name=region]:checked");
    let atts_to_aggregate = Array.prototype.slice.call(matches).reduce((a,t) => {
      a.push(['get', t.value])
      return a
    }, ['+'])
    this.state.map.setPaintProperty(
      'regions',
      'fill-opacity',
      ['/', atts_to_aggregate, atts_to_aggregate.length-1]
    )