atom/packages/git-diff/lib/main.js

const GitDiffView = require('./git-diff-view');
const DiffListView = require('./diff-list-view');

let diffListView = null;

module.exports = {
  activate() {
    const watchedEditors = new WeakSet();

    atom.workspace.observeTextEditors(editor => {
      if (watchedEditors.has(editor)) return;

      new GitDiffView(editor).start();
      atom.commands.add(
        atom.views.getView(editor),
        'git-diff:toggle-diff-list',
        () => {
          if (diffListView == null) diffListView = new DiffListView();
          diffListView.toggle();
        }
      );

      watchedEditors.add(editor);
      editor.onDidDestroy(() => watchedEditors.delete(editor));
    });
  },

  deactivate() {
    if (diffListView) diffListView.destroy();
    diffListView = null;
  }
};