let paintMode = false;
var myPolyline;

map.on('click', function() {
  paintMode = !paintMode;
  if (paintMode) {
    myPolyline = L.polyline([]).addTo(map);
  }
})

map.on('mousemove', function(e) {
  if (paintMode) {
    myPolyline.addLatLng(e.latlng);
  }
})

node:internal/modules/cjs/loader:488
      throw e;
      ^

Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './lib/tokenize' is not defined by "exports" in /Users/alisonqiu/Downloads/react-leaflet-examples/node_modules/postcss-safe-parser/node_modules/postcss/package.json
    at new NodeError (node:internal/errors:372:5)
    at throwExportsNotFound (node:internal/modules/esm/resolve:439:9)
    at packageExportsResolve (node:internal/modules/esm/resolve:718:3)
    at resolveExports (node:internal/modules/cjs/loader:482:36)
    at Function.Module._findPath (node:internal/modules/cjs/loader:522:31)
    at Function.Module._resolveFilename (node:internal/modules/cjs/loader:919:27)
    at Function.Module._load (node:internal/modules/cjs/loader:778:27)
    at Module.require (node:internal/modules/cjs/loader:999:19)
    at require (node:internal/modules/cjs/helpers:102:18)
    at Object.<anonymous> (/Users/alisonqiu/Downloads/react-leaflet-examples/node_modules/postcss-safe-parser/lib/safe-parser.js:1:17) {
  code: 'ERR_PACKAGE_PATH_NOT_EXPORTED'
}

Node.js v17.7.1