Also, we can avoid duplication of code using following structure:
```javascript

if (!this.videoProgressSlider.sliderRange) {
    this.videoProgressSlider.sliderRange = $('<div />', {
        class: "ui-slider-range ui-widget-header ui-corner-all slider-range"
    });

    this.videoProgressSlider.sliderProgress
        .after(this.videoProgressSlider.sliderRange);
}

this.videoProgressSlider.sliderRange
    .css({
        left: left + '%',
        width: width + '%'
    }); 
 ```