proj4 OpenLayers
            
import Map from 'ol/Map.js';import TileGrid from 'ol/tilegrid/TileGrid.js';
import View from 'ol/View.js';
import proj4 from 'proj4';
import {getCenter} from 'ol/extent.js';
import {get as getProjection} from 'ol/proj.js';
import {register} from 'ol/proj/proj4.js';
import GeoJSON from 'ol/format/GeoJSON.js';
import Graticule from 'ol/layer/Graticule.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import {Fill, Style} from 'ol/style.js';
...
        

            
proj4rs
            
import Map from 'ol/Map.js';import TileGrid from 'ol/tilegrid/TileGrid.js';
import View from 'ol/View.js';
import {proj4} from 'proj4rs/proj4.js';
import {getCenter} from 'ol/extent.js';
import {get as getProjection} from 'ol/proj.js';
import {register} from 'ol/proj/proj4.js';
import GeoJSON from 'ol/format/GeoJSON.js';
import Graticule from 'ol/layer/Graticule.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import {Fill, Style} from 'ol/style.js';
...