ES Module shims loader for intern (https://github.com/theintern/intern)

es-module-shims-loader.js

(function() {
  'use strict';

  intern.registerLoader(function(options) {
    if (intern.environment !== 'browser') {
      throw new Error('The ES Module Shims loader only works in the browser');
    }
    if (typeof options.esModulesShims !== 'string') {
      throw new Error(
        'The ES Module Shims loader requires "esModulesShims" to be of type ' +
          'string'
      );
    }

    intern.log('Initializing ES Module Shims loader with:', options);

    function resolveUrl(url) {
      if (url[0] !== '/' && !/https?:\/\//.test(url)) {
        url = `${intern.config.basePath}${url}`;
      }
      return url;
    }
    function addImportMap(srcOrObject) {
      const scriptTag = document.createElement('script');

      scriptTag.type = 'importmap-shim';
      if (typeof srcOrObject === 'string') {
        scriptTag.src = resolveUrl(srcOrObject);
      } else {
        scriptTag.text = JSON.stringify(srcOrObject);
      }
      const scriptTarget = document.head || document.body;

      scriptTarget.appendChild(scriptTag);
    }
    async function importModule(url) {
      return window.importShim(resolveUrl(url));
    }

    if (options.importMaps) {
      if (!Array.isArray(options.importMaps)) {
        if (
          typeof options.importMaps === 'string' ||
          typeof options.importMaps === 'object'
        ) {
          options.importMaps = [options.importMaps];
        } else {
          throw new Error(
            'The ES Module Shims loader requires "importMaps", if given, to ' +
              'be of a single (URL of the import map), and object (the import ' +
              'map itself) or an array of either'
          );
        }
      }
      options.importMaps.forEach(addImportMap);
    }

    return intern.loadScript(options.esModulesShims).then(function() {
      intern.log('Using ES Module Shims loader');

      return function(modules) {
        return Promise.all(modules.map(importModule));
      };
    });
  });
}());