Function scrollTween

src/playground.ts:42–48

(offset)

});

function scrollTween(offset) {
  return function() {
    let i = d3.interpolateNumber(window.pageYOffset ||
        document.documentElement.scrollTop, offset);
    return function(t) { scrollTo(0, i(t)); };
  };
}

const RECT_SIZE = 30;
const BIAS_SIZE = 5;