How to setState of one state using the state of another state onClick

Question

Is there a way to setState of one state with the state of another state? For example below in _updateData()...on click the geojson state gets the state of newGeojson? The goal is to be able to change the data={geojson} on click of the button (not showing the Geojson files in the example but let's say they exist in GeoJSON and newGeojson. I pull JSON from a firebase then convert it to GeoJSON in componentDidMount to create the geojson states). Thanks for the help. Hopefully, I am approaching this the right way.

import React from 'react';
import ReactMapGL, {Source, Layer} from 'react-map-gl';

class Map extends React.Component {
  state = {
    geojson: null,
    newGeojson: null,
  };

  _updateData() {
    // In here set the state of geojson to the state of newGeojson so the data={geojson} updates on click, something like setState{geojson} = newGeojson
  }

  render() {
    const {geojson} = this.state;

    return (
      <ReactMapGL latitude={37.78} longitude={-122.41} zoom={8}>
        <Source id="my-data" type="geojson" data={geojson}>
          <Layer
            id="point"
            type="circle"
            paint={{
              'circle-radius': 10,
              'circle-color': '#007cbf'
            }} />
        </Source>
        <button onClick={this._updateData()}>Update</button>
      </ReactMapGL>
    );
  }
}

Answer 1

Like that:

import React, { useState } from 'react';
import ReactMapGL, {Source, Layer} from 'react-map-gl';

const Map = () => {
  const [geojson, setGeojson] = useState(null)

  const updateData = () => {
    // for example
    fetch('url').then(resp => resp.json()).then(resp => {
      setGeojson(resp.data)
    })
  }

  return (
    <ReactMapGL latitude={37.78} longitude={-122.41} zoom={8}>
      <Source id="my-data" type="geojson" data={geojson}>
        <Layer
          id="point"
          type="circle"
          paint={{
            'circle-radius': 10,
            'circle-color': '#007cbf'
          }} />
      </Source>
      <button onClick={updateData}>Update</button>
    </ReactMapGL>
  );
}

It's using hooks. For old syntax you probably want this.setState({geojson: newGeojson}) (https://reactjs.org/docs/react-component.html#setstate)