JavaScript scoller start code.

Scroller.js

export default function(targetSelector, speed) {

    let current = (
        (document.documentElement.scrollTop || document.body.scrollTop)
        -
        (window.innerHeight / 2)
    );

    let target    = document.querySelector(targetSelector).getBoundingClientRect();
    let offset    = (target.bottom - (target.height / 2)) + current;
    let lastFrame = Date.now();

    let move = function() {
        let delta = (Date.now()-lastFrame) / 1000;
        lastFrame = Date.now();
        if (window.scrollY - offset >= 1) {
            return;
        }

        window.scrollBy(0, (offset * (delta * speed)));
        requestAnimationFrame(move);
    };

    move();
}