Is it necessary to have .slider::-webkit-slider-thumb in javascript?

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No, it is not necessary to have .slider::-webkit-slider-thumb in JavaScript.

The ::-webkit-slider-thumb is a CSS pseudo-element used to style the thumb of a range input slider in webkit-based browsers (such as Chrome and Safari).

JavaScript is used to manipulate the behavior and values of the slider, but the styling of the thumb can be achieved through CSS alone.

However, if you are using webkit-based browsers and want to customize the appearance of the slider thumb beyond what is available through CSS, then you may want to use this selector in your CSS.