Method on

src/common/events.js:13–22

(type, handle)

  }

  on(type, handle) {
    this.checkType(type);
    const { events } = this;
    let handlers = events[type];
    if (!handlers) {
      handlers = [];
      events[type] = handlers;
    }
    return () => this.off(type, handle);
  }

  off(type, handle) {
    this.checkType(type);