in extension.ts [79:90]
constructor(wordCounter: WordCounter) {
this._wordCounter = wordCounter;
this._wordCounter.updateWordCount();
// subscribe to selection change and editor activation events
let subscriptions: Disposable[] = [];
window.onDidChangeTextEditorSelection(this._onEvent, this, subscriptions);
window.onDidChangeActiveTextEditor(this._onEvent, this, subscriptions);
// create a combined disposable from both event subscriptions
this._disposable = Disposable.from(...subscriptions);
}