refactored Markdown components to reduce bundle size

static/js/directives/ui/markdown/markdown.module.ts

@@ -0,0 +1,72 @@
+import { NgModule } from 'ng-metadata/core';
+import { Converter, ConverterOptions } from 'showdown';
+import * as showdown from 'showdown';
+import { registerLanguage, highlightAuto } from 'highlight.js/lib/highlight';
+import 'highlight.js/styles/vs.css';
+const highlightedLanguages: string[] = require('../../../constants/highlighted-languages.constant.json');
+
+
+/**
+ * Dynamically fetch and register a new language with Highlight.js
+ */
+export const addHighlightedLanguage = (language: string): Promise<{}> => {
+  return new Promise((resolve, reject) => {
+    try {
+      // TODO(alecmerdler): Use `import()` here instead of `require()`
+      const langModule = require(`highlight.js/lib/languages/${language}`);
+      registerLanguage(language, langModule);
+      resolve();
+    } catch (error) {
+      console.log(`Language ${language} not supported for syntax highlighting`);
+      reject(error);
+    }
+  });
+};
+
+
+/**
+ * Showdown JS extension for syntax highlighting using Highlight.js
+ */
+export const showdownHighlight = (): showdown.FilterExtension => {
+  const htmlunencode = (text: string) => {
+    return (text
+      .replace(/&amp;/g, '&')
+      .replace(/&lt;/g, '<')
+      .replace(/&gt;/g, '>'));
+  };
+
+  const left = '<pre><code\\b[^>]*>';
+  const right = '</code></pre>';
+  const flags = 'g';
+  const replacement = (wholeMatch: string, match: string, leftSide: string, rightSide: string) => {
+    // TODO(alecmerdler): Call `addHighlightedLanguage` to load new languages that are detected using code-splitting
+    match = htmlunencode(match);
+    return leftSide + highlightAuto(match).value + rightSide;
+  };
+
+  return {
+    type: 'output',
+    filter: (text, converter, options) => {
+      return (<any>showdown).helper.replaceRecursiveRegExp(text, replacement, left, right, flags);
+    }
+  };
+};
+
+
+// Dynamically import syntax-highlighting supported languages
+highlightedLanguages.forEach((langName) => addHighlightedLanguage(langName));
+
+
+/**
+ * Markdown editor and view module.
+ */
+@NgModule({
+  imports: [],
+  declarations: [],
+  providers: [
+    {provide: 'markdownConverter', useValue: new Converter({extensions: [<any>showdownHighlight]})},
+  ],
+})
+export class MarkdownModule {
+
+}