it is a common trap you would fall when you were new to laravel .
laravel use webpack to compile all css and js files to app.css and app.js , if you want to import a new asset , import through npm or yarn , then run
npm run dev to compile them down.
for example , if you wanna use jquery in laravel project , first , npm install jquery.
then , in your resource/assets/js/app.js file , add a line :
import $ from 'jquery', compile , then good to go.
note that , resource/assets/js/app.js is not the same as public/js/app.js.