highlighter.ts

  /**
   * Highlight a selection on the page. `sel` is optional and mostly provided
   * for testing.
   */
  public async highlightCurrentSelection(rangyHighlighter:rangyHl.Highlighter, sel: Selection):
      Promise<models.HighlightedText> {
    const result: models.HighlightedText =
      this.createHighlightedTextFromSelection(rangy);

    // It looks like Rangy operates only on WrappedSelection. Faking it doesn't
    // seem trivial (at least three methods, some of which are non-obvious), and
    // WrappedSelection isn't an exported type. For now we'll just disregard the
    // sel parameter, which is ugly, but c'est la vie.
    sel = sel || this.rangyObj.getSelection(window);

    let highlights = rangyHighlighter.highlightSelection(HIGHLIGHT_CLASS_NAME);
    if (highlights.length > 1) {
      // Chrome only supports a single Range, according to the docs.
      throw new Error('More than one highlight, which should be impossible');
    }
    if (highlights.length == 0) {
      console.warn('No highlights returned');
    }

    return result;
  }