无法读取未定义的属性。 Jquery错误

Question

我正在研究reactjs。我收到了错误

Uncaught TypeError: Cannot read property 'left' of undefined
    at HTMLDivElement.eval (DummyPlayer.js:184)
    at HTMLDivElement.dispatch (dll.vendor.js:39569)
    at HTMLDivElement.elemData.handle (dll.vendor.js:39381)

以下是我的代码

return (

            <div>
                <div className='video-player'>
                    <div className='video-player-inner'>
                        <video
                            className='video-js video-el vjs-big-play-centered vjs-default-skin'
                            id='video-el'
                            ref={node => this.video_el = node}>
                            <source src={this.props.video_file_selected_reducer.url} type="video/mp4"/>
                        </video>
                    </div>
                </div>
                <div id="custom-seekbar" onClick={this.customBarClicked}>
                    <span></span>
                </div>
            </div>

        )

这是我的customBarClicked方法

customBarClicked(e){
        var offset = $(this).offset();
        var left = (e.pageX - offset.left);
        var totalWidth = $("#custom-seekbar").width();
       var percentage = ( left / totalWidth );
        var vidTime = duration * percentage;
        currentTime = vidTime;
    }

有人可以告诉我如何解决它吗？