Custom webpack chunk loading from a web extension (Chrome) content script.

background.js

// Throw this in your background script, it injects a generated webpack chunk when asked
chrome.runtime.onMessage.addListener(function ({ type, data}, sender, sendResponse) {
  if (type === 'requestFileInjection') {
    const file = data.fileName
    if (!file) throw new Error('No file name provided.')
    chrome.tabs.executeScript({ file: `${file}.js` }, (result) => {
      console.log(`${file}.js injected`)
      return sendResponse({ type: 'injected', target: { src: `${file}.js` }, success: true })
    })
    return true // return true so sendResponse stays valid
  }
})

customLoader.js

// Import at the top of your entry file, it requests an injection from the background script.
var installedChunks = {
  "page": 0
};

__webpack_require__.e = function requireEnsure(chunkId) {
  var promises = [];


  // JSONP chunk loading for javascript

  var installedChunkData = installedChunks[chunkId];
  if (installedChunkData !== 0) { // 0 means "already installed".

    // a Promise means "currently loading".
    if (installedChunkData) {
      promises.push(installedChunkData[2]);
    } else {
      // setup Promise in chunk cache
      var promise = new Promise(function (resolve, reject) {
        installedChunkData = installedChunks[chunkId] = [resolve, reject];
      });
      promises.push(installedChunkData[2] = promise);

      // create error before stack unwound to get useful stacktrace later
      var error = new Error();
      onScriptComplete = function (event) {
        // if type is injected & success set chunk to loaded and resolve promise
        if (event && event.type === 'injected' && event.success === true) { installedChunks[chunkId][0](); installedChunks[chunkId] = 0 };
        // avoid mem leaks in IE.
        window.clearTimeout(timeout);
        var chunk = installedChunks[chunkId];
        if (chunk !== 0) {
          if (chunk) {
            var errorType = event && (event.type === 'load' ? 'missing' : event.type);
            var realSrc = event && event.target && event.target.src;
            error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realSrc + ')';
            error.name = 'ChunkLoadError';
            error.type = errorType;
            error.request = realSrc;
            chunk[1](error);
          }
          installedChunks[chunkId] = undefined;
        }
      };
      var timeout = setTimeout(function () {
        onScriptComplete({
          type: 'timeout'
        });
      }, 120000);

      // start chunk loading
      chrome.runtime.sendMessage({ type: "requestFileInjection", data: { fileName: chunkId } }, onScriptComplete)
    }
  }
  return Promise.all(promises);
};