working but incomplete version with new build.

dist/external/dynamic-import-polyfill/importModule.js

@@ -0,0 +1,176 @@
+/* eslint-disable jsdoc/require-file-overview */
+/**
+ * Adapted from {@link https://github.com/uupaa/dynamic-import-polyfill/blob/master/importModule.js}.
+ * @module importModule
+ * @license MIT
+ */
+
+/**
+ * Converts a possible relative URL into an absolute one.
+ * @param {string} url
+ * @returns {string}
+ */
+function toAbsoluteURL (url) {
+  const a = document.createElement('a');
+  a.setAttribute('href', url); // <a href="hoge.html">
+  return a.cloneNode(false).href; // -> "http://example.com/hoge.html"
+}
+
+/**
+ * Add any of the whitelisted attributes to the script tag.
+ * @param {HTMLScriptElement} script
+ * @param {PlainObject<string, string>} atts
+ * @returns {void}
+ */
+function addScriptAtts (script, atts) {
+  ['id', 'class', 'type'].forEach((prop) => {
+    if (prop in atts) {
+      script[prop] = atts[prop];
+    }
+  });
+}
+
+// Additions by Brett
+/**
+* @typedef {PlainObject} module:importModule.ImportConfig
+* @property {string} global The variable name to set on `window` (when not using the modular version)
+* @property {boolean} [returnDefault=false]
+*/
+
+/**
+* @function module:importModule.importSetGlobalDefault
+* @param {string|GenericArray<any>} url
+* @param {module:importModule.ImportConfig} config
+* @returns {Promise<any>} The value to which it resolves depends on the export of the targeted module.
+*/
+export function importSetGlobalDefault (url, config) {
+  return importSetGlobal(url, {...config, returnDefault: true});
+}
+/**
+* @function module:importModule.importSetGlobal
+* @param {string|string[]} url
+* @param {module:importModule.ImportConfig} config
+* @returns {Promise<ArbitraryModule>} The promise resolves to either an `ArbitraryModule` or
+*   any other value depends on the export of the targeted module.
+*/
+export async function importSetGlobal (url, {global: glob, returnDefault}) {
+  // Todo: Replace calls to this function with `import()` when supported
+  const modularVersion = !('svgEditor' in window) ||
+    !window.svgEditor ||
+    window.svgEditor.modules !== false;
+  if (modularVersion) {
+    return importModule(url, undefined, {returnDefault});
+  }
+  await importScript(url);
+  return window[glob];
+}
+
+/**
+ *
+ * @author Brett Zamir (other items are from `dynamic-import-polyfill`)
+ * @param {string|string[]} url
+ * @param {PlainObject} [atts={}]
+ * @returns {Promise<void|Error>} Resolves to `undefined` or rejects with an `Error` upon a
+ *   script loading error
+ */
+export function importScript (url, atts = {}) {
+  if (Array.isArray(url)) {
+    return Promise.all(url.map((u) => {
+      return importScript(u, atts);
+    }));
+  }
+  return new Promise((resolve, reject) => { // eslint-disable-line promise/avoid-new
+    const script = document.createElement('script');
+    /**
+     *
+     * @returns {void}
+     */
+    function scriptOnError () {
+      reject(new Error(`Failed to import: ${url}`));
+      destructor();
+    }
+    /**
+     *
+     * @returns {void}
+     */
+    function scriptOnLoad () {
+      resolve();
+      destructor();
+    }
+    const destructor = () => {
+      script.removeEventListener('error', scriptOnError);
+      script.removeEventListener('load', scriptOnLoad);
+      script.remove();
+      script.src = '';
+    };
+    script.defer = 'defer';
+    addScriptAtts(script, atts);
+    script.addEventListener('error', scriptOnError);
+    script.addEventListener('load', scriptOnLoad);
+    script.src = url;
+
+    document.head.append(script);
+  });
+}
+
+/**
+*
+* @param {string|string[]} url
+* @param {PlainObject} [atts={}]
+* @param {PlainObject} opts
+* @param {boolean} [opts.returnDefault=false} = {}]
+* @returns {Promise<any>} Resolves to value of loading module or rejects with
+*   `Error` upon a script loading error.
+*/
+export function importModule (url, atts = {}, {returnDefault = false} = {}) {
+  if (Array.isArray(url)) {
+    return Promise.all(url.map((u) => {
+      return importModule(u, atts);
+    }));
+  }
+  return new Promise((resolve, reject) => { // eslint-disable-line promise/avoid-new
+    const vector = '$importModule$' + Math.random().toString(32).slice(2);
+    const script = document.createElement('script');
+    /**
+     *
+     * @returns {void}
+     */
+    function scriptOnError () {
+      reject(new Error(`Failed to import: ${url}`));
+      destructor();
+    }
+    /**
+     *
+     * @returns {void}
+     */
+    function scriptOnLoad () {
+      resolve(window[vector]);
+      destructor();
+    }
+    const destructor = () => {
+      delete window[vector];
+      script.removeEventListener('error', scriptOnError);
+      script.removeEventListener('load', scriptOnLoad);
+      script.remove();
+      URL.revokeObjectURL(script.src);
+      script.src = '';
+    };
+    addScriptAtts(script, atts);
+    script.defer = 'defer';
+    script.type = 'module';
+    script.addEventListener('error', scriptOnError);
+    script.addEventListener('load', scriptOnLoad);
+    const absURL = toAbsoluteURL(url);
+    const loader = `import * as m from '${
+      absURL.replace(/'/g, "\\'")
+    }'; window.${vector} = ${
+      returnDefault ? 'm.default || ' : ''
+    }m;`; // export Module
+    const blob = new Blob([loader], {type: 'text/javascript'});
+    script.src = URL.createObjectURL(blob);
+
+    document.head.append(script);
+  });
+}
+
+export default importModule;