JS mouseMove speed

let timestamp = null;
let lastMouseX = null;
let lastMouseY = null;
let speedX;
let speedY;

document .addEventListener("mousemove", function(e) {
    if (timestamp === null) {
        timestamp = Date.now();
        lastMouseX = e.screenX;
        lastMouseY = e.screenY;
        return;
    }

    let now = Date.now();
    let dt =  now - timestamp;
    let dx = e.screenX - lastMouseX;
    let dy = e.screenY - lastMouseY;
    speedX = Math.round(dx / dt * 100);
    speedY = Math.round(dy / dt * 100);

    timestamp = now;
    lastMouseX = e.screenX;
    lastMouseY = e.screenY;

});