Steps to reproduce

1. rails new actiontexttest --webpacker
2. cd actiontexttest
3. rails action_text:install
4. rails db:migrate RAILS_ENV=development
5. Add a root route, controller and view file
6. bin/rails server
7. bin/webpack-dev-server
8. goto http://localhost:3000 (in Internet Explorer 11)

Expected behavior

No error to be raised.

Actual behavior

Error being raised in Internet Explorer 11's console:

SCRIPT1002: Syntax error
File: application.js, Line: 10452, Column: 1

Line 10452 in my case being:

/***/ "./node_modules/@rails/actiontext/app/javascript/actiontext/attachment_upload.js":
/*!***************************************************************************************!*\
  !*** ./node_modules/@rails/actiontext/app/javascript/actiontext/attachment_upload.js ***!
  \***************************************************************************************/
/*! exports provided: AttachmentUpload */
/***/ (function(module, __webpack_exports__, __webpack_require__) {

"use strict";
__webpack_require__.r(__webpack_exports__);
/* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "AttachmentUpload", function() { return AttachmentUpload; });
/* harmony import */ var _rails_activestorage__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! @rails/activestorage */ "./node_modules/@rails/activestorage/app/assets/javascripts/activestorage.js");
/* harmony import */ var _rails_activestorage__WEBPACK_IMPORTED_MODULE_0___default = /*#__PURE__*/__webpack_require__.n(_rails_activestorage__WEBPACK_IMPORTED_MODULE_0__);

class AttachmentUpload {
  constructor(attachment, element) {
    this.attachment = attachment
    this.element = element
    this.directUpload = new _rails_activestorage__WEBPACK_IMPORTED_MODULE_0__["DirectUpload"](attachment.file, this.directUploadUrl, this)
  }

…

Reflections

Works fine with above reproduction steps (rails 6.0.1) but not on Dockspot with 6.0.0) It looks like the class keyword was not transpired, causing a syntax error in IE's old parser.

System configuration

Rails version: 6.0.0

Ruby version: 2.6.3p62

package.json:

{
  "engines": {
    "node": "10.16.0",
    "yarn": "^1.17.3",
    "npm": "^6.11.2"
  },
  "dependencies": {
    "@babel/core": "^7.6.4",
    "@babel/preset-react": "^7.6.3",
    "@rails/actiontext": "^6.0.0",
    "@rails/webpacker": "^4.0.7",
    "@stimulus/polyfills": "^1.1.1",
    "mutationobserver-shim": "^0.3.3",
    "stimulus": "^1.1.1",
    "trix": "^1.2.1",
    "uglifyjs-webpack-plugin": "^2.2.0"
  },
  "devDependencies": {
    "webpack-cli": "^3.3.10",
    "webpack-dev-server": "^3.9.0"
  }
}

.browserslistrc

defaults

npx browserslist

chrome 78
edge 18
firefox 70
ie 11
opera 62
safari 13

… (and more)

Question

Has anyone else encountered errors with ActionText not transpiling to compatible javascript defined by