Bootstrap 4: Uncaught ReferenceError: Popper is not defined
Since our Bootstrap beta 2 release, we added two new dist files : bootstrap.bundle.js and bootstrap.bundle.min.js which contain Popper.js inside
Plus use this link to find the latest release of Popper.js : https://cdnjs.com/libraries/popper.js because the above linked release (1.8.2) is very old, latest is 1.12.9
BTW you should choose the UMD release of Popper.js because it's the one used by Bootstrap
Use bootstrap.bundle.js that already has popper.js NPM path 'bootstrap/dist/js/bootstrap.bundle.js'.
For those struggling with this issue on Webpack: In your entry file,
import 'bootstrap' does give the error. You need to remove that and replace it with import 'bootstrap/dist/js/bootstrap.bundle.js'
This is sufficient and you don't need to import Popper separately. That applies for bootstrap 4.0.0.beta2