react-leaflet, markers re-render when the popup is opened/closed

Question

The problem is that every time I hover on a marker a popup is opened or closed and it causes all the markers to re-render even though my state is not changing. console.log(myState); is running every time I hover in and out of the marker.

I tried to use useMemo hook but couldn't figure out how to use it on country.map. Any help?

Here is my code:

import React, { useEffect, useState } from 'react';
import { Map, TileLayer, Marker, Popup } from 'react-leaflet';
import axios from 'axios';
import { v4 as uuidv4 } from 'uuid';
import { Icon } from 'leaflet';

const myicon = new Icon({
  iconUrl: './icon.svg',
  iconSize: [20, 20]
});

const MyMap = () => {
  const [myState, setMyState] = useState(null);
  const [activePlace, setActivePlace] = useState(null);

  const getData = async () => {
    let response = await axios
      .get('https://corona.lmao.ninja/v2/jhucsse')
      .catch(err => console.log(err));

    let data = response.data;
    setMyState(data);

    // console.log(data);
  };

  useEffect(() => {
    getData();
  }, []);

  if (myState) {
    console.log(myState);
    return (
        <Map
          style={{ height: '100vh', width: '100vw' }}
          center={[14.561, 17.102]}
          zoom={1}
        >
          <TileLayer
            attribution='&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors &copy; <a href="https://carto.com/attributions">CARTO</a>'
            url={
              'https://{s}.basemaps.cartocdn.com/dark_all/{z}/{x}/{y}{r}.png'
            }
          />

          {myState.map(country => {
            return (
              <Marker
                key={uuidv4()}
                position={[
                  country.coordinates.latitude,
                  country.coordinates.longitude
                ]}
                onmouseover={() => {
                  setActivePlace(country);
                }}
                onmouseout={() => {
                  setActivePlace(null);
                }}
                icon={myicon}
              />
            );
          })}

          {activePlace && (
            <Popup
              position={[
                activePlace.coordinates.latitude,
                activePlace.coordinates.longitude
              ]}
            >
              <div>
                <h4>Country: {activePlace.country}</h4>
              </div>
            </Popup>
          )}
        </Map>
    );
  } else {
    return <div>Nothing</div>;
  }
};

export default MyMap;

Answer 1

Do you even need myState to be state? Can it just be a regular variable? That would solve your issue right away. If not, make a copy of myState, and then run map() with that. You will also need a flag to determine whether or not to run the map function, so setup a runMap state hook:

const MyMap = () => {

  // *** Create a FLAG for the map() call
  const [runMap, setRunMap] = useState(false);
  const [activePlace, setActivePlace] = useState(null);

  // setup the data to be function-scoped
  let data;

  const getData = async () => {
    let response = await axios
      .get('https://corona.lmao.ninja/v2/jhucsse')
      .catch(err => console.log(err));

    // just use the data here
    data = response.data;

    // set your runMap flag
    setRunMap(true);
  }

// later on...

if (runMap) {

// ...

  {data.map(country => {

As a side-note, you aren't supposed to be calling hooks this way, inside of nested functions and all. They are supposed to be called at the top-level of the component. There are a bunch of rules honestly, in your case it seems like using a class-based component and replacing your useEffect hook with componentDidMount might be safer, with the downside of being more verbose.