Popper not working in Beta 4

[MWDelaney]

Submit a feature request or bug report

• I've read the guidelines for Contributing to Roots Projects
• This is a feature request
• This is a bug report
• This request isn't a duplicate of an existing issue
• I've read the docs and NPM Debugging Guidelines post and followed them (if applicable)
• This is not a personal support request that should be posted on the Roots Discourse forums

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What is the current behavior?

Popper (required by Bootstrap 4 Beta for dropdowns) is not working in Sage9 Beta 4. I banged my head against an existing theme I'd ported into Beta 4 for a while with no luck, and eventually tried a plain vanilla Beta 4 and found the same results.

Upon clicking a dropdown trigger, I get the following message:

TypeError: Object is not a constructor (evaluating 'new Popper(element, this._menu, this._getPopperConfig())')

I tried importing Popper in main.js and nothing changed.

What is the expected or desired behavior?

Popper should work, as it's required for Bootstrap 4 functionality.

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Bug report

Please provide steps to reproduce, including full log output:

1. Install a fresh copy of Sage9 Beta 4 with composer, run basic setup and yarn steps
2. Add the following Bootstrap 4 example code to a view:

<div class="dropdown">
  <button class="btn btn-secondary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Dropdown button
  </button>
  <div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
    <a class="dropdown-item" href="#">Action</a>
    <a class="dropdown-item" href="#">Another action</a>
    <a class="dropdown-item" href="#">Something else here</a>
  </div>
</div>

3. Rerun yarn build and see the console errors when you try to trigger the dropdown.

Please describe your local environment:

WordPress version: 4.8.1

OS: MacOS X

NPM/Node version: v7.4.0

Where did the bug happen? Development or remote servers?

Development

Is there a related Discourse thread or were any utilized (please link them)?

No

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