HRM runtime calls window.location.reload(), breaks in in web worker context

[clintharris]

🐛 bug report

HMR update events are currently causing ReferenceError: window does not exist in browser-targeted apps that use web workers.

This appears to be happening because hrm-runtime.js makes reference to the window global, which doesn't exist in a web worker context:

if (handled) {
  console.clear();

  data.assets.forEach(function (asset) {
    hmrApply(global.parcelRequire, asset);
  });

  assetsToAccept.forEach(function (v) {
    hmrAcceptRun(v[0], v[1]);
  });
} else {
  window.location.reload(); 👈 But window doesn't exist in web worker context! 😭
}

🤔 Expected Behavior

No error should be encountered by web worker code when an HMR update occurs.

😯 Current Behavior

ReferenceError: window does not exist

💻 Code Sample

1. Clone https://github.com/clintharris/parcel-hrm-bug-demo
2. npm install && npm start
3. Load http://localhost:1234, open browser JS console.
4. Edit src/index.js to trigger HMR update.
5. JS console error: ReferenceError: window is not defined

🌍 Your Environment

Software	Version(s)
Parcel	1.12.3
Node	12.3
npm/Yarn	npm 6.4