JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <body style="height:9999px;">
        <div id="fading" style="margin-top:200px;background:#aaa;">Fading</div>
    </body>
</html>

JavaScript

var fadeStart=100 // 100px scroll or less will equiv to 1 opacity
    ,fadeUntil=200 // 200px scroll or more will equiv to 0 opacity
    ,fading = $('#fading')
;

$(window).bind('scroll', function(){
    var offset = $(document).scrollTop()
        ,opacity=0
    ;
    if( offset<=fadeStart ){
        opacity=1;
    }else if( offset<=fadeUntil ){
        opacity=1-offset/fadeUntil;
    }
    fading.css('opacity',opacity).html(opacity);
});