Method on

dash/dash-renderer/src/actions/utils.js:177–181

(event, listener)

        this._ev = {};
    }
    on(event, listener) {
        const events = (this._ev[event] = this._ev[event] || []);
        events.push(listener);
        return () => this.removeListener(event, listener);
    }
    removeListener(event, listener) {
        const events = this._ev[event];
        if (events) {