Method once

packages/fairygui/src/core/Timer.ts:145–147

* Execute callback after specified delay (one time) * 延迟执行回调（一次） * * @param delay Delay in milliseconds | 延迟时间（毫秒） * @param caller Callback context | 回调上下文 * @param callback Callback function | 回调函数

(delay: number, caller: any, callback: Function)

     * @param callback Callback function | 回调函数
     */
    public once(delay: number, caller: any, callback: Function): void {
        this.addCallback(delay, caller, callback, false);
    }

    /**
     * Execute callback repeatedly at interval