smoothScroll.js

[
    
    { trigger: ".btn1", target: "section1", offset: 0, speed: 1000 },
    { trigger: ".btn2", target: "section2", offset: 0, speed: 1000 },
    { trigger: ".btn3", target: "section3", offset: 0, speed: 1000 }

    
].forEach(({ trigger, target, offset, speed }) => {
    document.querySelectorAll(trigger).forEach(button => {
        button.addEventListener("click", () => {
            const start = window.scrollY,
                  end = document.getElementById(target).offsetTop - offset,
                  t0 = performance.now();
            requestAnimationFrame(function step(t) {
                const p = Math.min((t - t0) / speed, 1),
                      e = p < .5 ? 2 * p * p : 1 - Math.pow(-2 * p + 2, 2) / 2;
                window.scrollTo(0, start + (end - start) * e);
                if (p < 1) requestAnimationFrame(step);
            });
        });
    });
});