lunr.js: Incompatible with ES6 Modules

I’m unable to load Lunr.js in an ES6 module. I know Lunr isn’t packaged up in an ES6 module, but imported scripts will still cause side effects and the window.lunr global can be used within an ES6 module [stack overflow] [codepen example]:

import "https://unpkg.com/lunr/lunr.js"

var documents = [{ 
  "name": "Lunr",
  "text": "Like Solr, but much smaller, and not as bright."
}, {
  "name": "React",
  "text": "A JavaScript library for building user interfaces."
}, {
  "name": "Lodash",
  "text": "A modern JavaScript utility library delivering modularity, performance & extras."
}]

const lunr = window.lunr

var idx = lunr(function () {
  this.ref('name')
  this.field('text')

  documents.forEach(function (doc) {
    this.add(doc)
  }, this)
})

console.log(idx.search("bright"))

This results in an error: Uncaught TypeError: Cannot set property 'lunr' of undefined. on line 3461 root.lunr = factory()