From what I've read so far, popper.js is a big pain with Bootstrap 4. I can't get it to work. I keep getting this error:

> 
> Error: Bootstrap dropdown require Popper.js (<https://popper.js.org>)
> 
> 
> 

I've tried the CDN and NPM install. Same result. At the bottom of my HTML file, I have this for the NPM install:

```
<script src="js/jquery.min.js"></script>
<script src="js/popper.min.js"></script>
<script src="js/tether.min.js"></script>
<script src="js/bootstrap.min.js"></script>

```

Then tried this for the CDN:

```
<script src="/js/jquery.min.js"></script>
<script src="/js/tether.min.js"></script>
<script src="https://cdnjs.com/libraries/popper.js"></script>
<script src="/js/bootstrap.min.js"></script>

```

Any ideas what I'm doing wrong?