JSFiddle - React, Tailwind, and code Playground

HTML

<span>Update speed</span>
<br>
Current speed: <span id="speed">0</span> pixels/s

JavaScript

var timestamp = 0;
var mY = 0;
$(document).mousemove(function(e) {
    var now = Date.now();
    currentmY = e.screenY;

	  var dt = now - timestamp;
    var distance = Math.abs(currentmY - mY);
    var speed = Math.round(distance / dt * 1000);
    console.log(dt, distance, speed);
    document.getElementById("speed").innerHTML = speed;
    
    mY = currentmY;
    timestamp = now;
});