2,ol-ext扩展

openlayers的扩展有两个，一定要切记！ 分别对应不同的使用情况！

NPM packages

ol-ext exist as ES6 modules (ol-ext) and as pure js (openlayers-ext).

using ol-ext in a webpack

• For use with webpack, Rollup, Browserify, or other module bundlers, install the npm ol-ext package and link to the node_modules directory:

npm install ol-ext

See the following examples for more detail on bundling OpenLayers with your application:

• Using webpack
• Using parcel
• Using parcel

using ol-ext in a web page

• For use in a web page install the npm openlayers-ext package:

npm install openlayers-ext