Method one

src/watcher.ts:242–244

(event: EventName, callback: Listener)

        }
    }
    one(event: EventName, callback: Listener) {
        this.on(event, callback, true);
    }
    recalculateSize() {
        if (this.watchItem instanceof HTMLElement) {
            this.height = this.watchItem.offsetHeight + this.offsets.top + this.offsets.bottom;