use Webpack code-splitting to dynamically import Highlight.js languages as they are detected by Showdown Markdown extension

static/js/directives/ui/markdown/markdown-editor.component.spec.ts

@@ -29,6 +29,16 @@ describe("MarkdownEditorComponent", () => {
     });
   });
 
+  describe("ngOnDestroy", () => {
+
+    it("removes 'beforeunload' event listener", () => {
+      $windowMock.setup(mock => mock.onbeforeunload).is(() => 1);
+      component.ngOnDestroy();
+
+      expect($windowMock.Object.onbeforeunload.call(this)).toEqual(null);
+    });
+  });
+
   describe("changeEditMode", () => {
 
     it("sets component's edit mode to given mode", () => {
@@ -147,7 +157,15 @@ describe("MarkdownEditorComponent", () => {
 
   describe("discardChanges", () => {
 
-    it("emits output event with no content", (done) => {
+    it("prompts user to confirm discarding changes", () => {
+      const confirmSpy: Spy = $windowMock.setup(mock => mock.confirm).is((message) => false).Spy;
+      component.discardChanges();
+
+      expect(confirmSpy.calls.argsFor(0)[0]).toEqual(`Are you sure you want to discard your changes?`);
+    });
+
+    it("emits output event with no content if user confirms discarding changes", (done) => {
+      $windowMock.setup(mock => mock.confirm).is((message) => true);
       component.discard.subscribe((event: {}) => {
         expect(event).toEqual({});
         done();
@@ -155,5 +173,16 @@ describe("MarkdownEditorComponent", () => {
 
       component.discardChanges();
     });
+
+    it("does not emit output event if user declines confirmation of discarding changes", (done) => {
+      $windowMock.setup(mock => mock.confirm).is((message) => false);
+      component.discard.subscribe((event: {}) => {
+        fail(`Should not emit output event`);
+        done();
+      });
+
+      component.discardChanges();
+      done();
+    });
   });
 });

static/js/directives/ui/markdown/markdown-editor.component.ts

@@ -1,4 +1,4 @@
-import { Component, Inject, Input, Output, EventEmitter, ViewChild, HostListener } from 'ng-metadata/core';
+import { Component, Inject, Input, Output, EventEmitter, ViewChild, HostListener, OnDestroy } from 'ng-metadata/core';
 import { MarkdownSymbol } from '../../../types/common.types';
 import { BrowserPlatform } from '../../../constants/platform.constant';
 import './markdown-editor.component.css';
@@ -11,7 +11,7 @@ import './markdown-editor.component.css';
   selector: 'markdown-editor',
   templateUrl: '/static/js/directives/ui/markdown/markdown-editor.component.html'
 })
-export class MarkdownEditorComponent {
+export class MarkdownEditorComponent implements OnDestroy {
 
   @Input('<') public content: string;
 
@@ -34,6 +34,10 @@ export class MarkdownEditorComponent {
     return false;
   }
 
+  public ngOnDestroy(): void {
+    this.$window.onbeforeunload = () => null;
+  }
+
   public changeEditMode(newMode: EditMode): void {
     this.editMode = newMode;
   }
@@ -110,7 +114,9 @@ export class MarkdownEditorComponent {
   }
 
   public discardChanges(): void {
-    this.discard.emit({});
+    if (this.$window.confirm(`Are you sure you want to discard your changes?`)) {
+      this.discard.emit({});
+    }
   }
 
   public get currentEditMode(): EditMode {

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

@@ -1,5 +1,5 @@
 import { NgModule } from 'ng-metadata/core';
-import { Converter, ConverterOptions } from 'showdown';
+import { Converter } from 'showdown';
 import * as showdown from 'showdown';
 import { registerLanguage, highlightAuto } from 'highlight.js/lib/highlight';
 import 'highlight.js/styles/vs.css';
@@ -10,14 +10,15 @@ const highlightedLanguages: string[] = require('../../../constants/highlighted-l
  * Dynamically fetch and register a new language with Highlight.js
  */
 export const addHighlightedLanguage = (language: string): Promise<{}> => {
-  return new Promise((resolve, reject) => {
+  return new Promise(async(resolve, reject) => {
     try {
-      // TODO(alecmerdler): Use `import()` here instead of `require()`
-      const langModule = require(`highlight.js/lib/languages/${language}`);
+      // TODO(alecmerdler): Use `import()` here instead of `System.import()` after upgrading to TypeScript 2.4
+      const langModule = await System.import(`highlight.js/lib/languages/${language}`);
       registerLanguage(language, langModule);
+      console.debug(`Language ${language} registered for syntax highlighting`);
       resolve();
     } catch (error) {
-      console.log(`Language ${language} not supported for syntax highlighting`);
+      console.debug(`Language ${language} not supported for syntax highlighting`);
       reject(error);
     }
   });
@@ -25,7 +26,7 @@ export const addHighlightedLanguage = (language: string): Promise<{}> => {
 
 
 /**
- * Showdown JS extension for syntax highlighting using Highlight.js
+ * Showdown JS extension for syntax highlighting using Highlight.js. Will attempt to register detected languages.
  */
 export const showdownHighlight = (): showdown.FilterExtension => {
   const htmlunencode = (text: string) => {
@@ -39,7 +40,10 @@ export const showdownHighlight = (): showdown.FilterExtension => {
   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
+    const language: string = leftSide.slice(leftSide.indexOf('language-') + ('language-').length,
+                                            leftSide.indexOf('"', leftSide.indexOf('language-')));
+    addHighlightedLanguage(language).catch(error => null);
+
     match = htmlunencode(match);
     return leftSide + highlightAuto(match).value + rightSide;
   };
@@ -53,7 +57,7 @@ export const showdownHighlight = (): showdown.FilterExtension => {
 };
 
 
-// Dynamically import syntax-highlighting supported languages
+// Import default syntax-highlighting supported languages
 highlightedLanguages.forEach((langName) => addHighlightedLanguage(langName));