Web Components: Add script tag support

app/web-components/src/client/preview/helpers/simulate-pageload.ts

@@ -0,0 +1,97 @@
+import { document } from 'global';
+
+// https://html.spec.whatwg.org/multipage/scripting.html
+const runScriptTypes = [
+  'application/javascript',
+  'application/ecmascript',
+  'application/x-ecmascript',
+  'application/x-javascript',
+  'text/ecmascript',
+  'text/javascript',
+  'text/javascript1.0',
+  'text/javascript1.1',
+  'text/javascript1.2',
+  'text/javascript1.3',
+  'text/javascript1.4',
+  'text/javascript1.5',
+  'text/jscript',
+  'text/livescript',
+  'text/x-ecmascript',
+  'text/x-javascript',
+];
+
+const SCRIPT = 'script';
+const SCRIPTS_ROOT_ID = 'scripts-root';
+
+// trigger DOMContentLoaded
+export function simulateDOMContentLoaded() {
+  const DOMContentLoadedEvent = document.createEvent('Event');
+  DOMContentLoadedEvent.initEvent('DOMContentLoaded', true, true);
+  document.dispatchEvent(DOMContentLoadedEvent);
+}
+
+function insertScript($script: any, callback: any, $scriptRoot: any) {
+  const scriptEl = document.createElement('script');
+  scriptEl.type = 'text/javascript';
+  if ($script.src) {
+    scriptEl.onload = callback;
+    scriptEl.onerror = callback;
+    scriptEl.src = $script.src;
+  } else {
+    scriptEl.textContent = $script.innerText;
+  }
+
+  // re-insert the script tag so it executes.
+  if ($scriptRoot) $scriptRoot.appendChild(scriptEl);
+  else document.head.appendChild(scriptEl);
+
+  // clean-up
+  $script.parentNode.removeChild($script);
+
+  // run the callback immediately for inline scripts
+  if (!$script.src) callback();
+}
+
+// runs an array of async functions in sequential order
+/* eslint-disable no-param-reassign, no-plusplus */
+function insertScriptsSequentially(scriptsToExecute: any[], callback: any, index = 0) {
+  scriptsToExecute[index](() => {
+    index++;
+    if (index === scriptsToExecute.length) {
+      callback();
+    } else {
+      insertScriptsSequentially(scriptsToExecute, callback, index);
+    }
+  });
+}
+
+export function simulatePageLoad($container: any) {
+  let $scriptsRoot = document.getElementById(SCRIPTS_ROOT_ID);
+  if (!$scriptsRoot) {
+    $scriptsRoot = document.createElement('div');
+    $scriptsRoot.id = SCRIPTS_ROOT_ID;
+    document.body.appendChild($scriptsRoot);
+  } else {
+    $scriptsRoot.innerHTML = '';
+  }
+  const $scripts = Array.from($container.querySelectorAll(SCRIPT));
+
+  if ($scripts.length) {
+    const scriptsToExecute: any[] = [];
+    $scripts.forEach(($script: any) => {
+      const typeAttr = $script.getAttribute('type');
+
+      // only run script tags without the type attribute
+      // or with a javascript mime attribute value
+      if (!typeAttr || !runScriptTypes.includes(typeAttr)) {
+        scriptsToExecute.push((callback: any) => insertScript($script, callback, $scriptsRoot));
+      }
+    });
+
+    // insert the script tags sequentially
+    // to preserve execution order
+    insertScriptsSequentially(scriptsToExecute, simulateDOMContentLoaded, undefined);
+  } else {
+    simulateDOMContentLoaded();
+  }
+}

app/web-components/src/client/preview/render.ts

@@ -2,6 +2,7 @@ import { document, Node } from 'global';
 import dedent from 'ts-dedent';
 import { render, TemplateResult } from 'lit-html';
 import { RenderContext } from './types';
+import { simulatePageLoad, simulateDOMContentLoaded } from './helpers/simulate-pageload';
 
 const rootElement = document.getElementById('root');
 
@@ -26,8 +27,10 @@ export default function renderMain({
     const renderTo = rootElement.querySelector('[id="root-inner"]');
 
     render(element, renderTo);
+    simulatePageLoad(rootElement);
   } else if (typeof element === 'string') {
     rootElement.innerHTML = element;
+    simulatePageLoad(rootElement);
   } else if (element instanceof Node) {
     // Don't re-mount the element if it didn't change and neither did the story
     if (rootElement.firstChild === element && forceRender === true) {
@@ -36,6 +39,7 @@ export default function renderMain({
 
     rootElement.innerHTML = '';
     rootElement.appendChild(element);
+    simulateDOMContentLoaded();
   } else {
     showError({
       title: `Expecting an HTML snippet or DOM node from the story: "${name}" of "${kind}".`,

examples/web-components-kitchen-sink/stories/script.stories.js

@@ -0,0 +1,13 @@
+import { html } from 'lit-html';
+
+export default {
+  title: 'Script Tag',
+};
+
+export const inTemplate = () =>
+  html`<div>JS alert</div>
+    <script>
+      alert('hello');
+    </script>`;
+
+export const inString = () => '<div>JS alert</div><script>alert("hello")</script>';