export function loadExtension(extensionModule) {
  let extension
  if (typeof extensionModule === 'string') {
    extension = require(extensionModule)
  } else {
    extension = extensionModule
  }
  if (extension == null || typeof extension !== 'object') {
    throw new Error(
      `Expected ${extensionModule} to export an extension but instead ` +
        `got: ${extension}`
    )
  } else if (extension.default) {
    // ECMAScript module interop.
    extension = extension.default
  }
  return extension
}