Weighted eases

Here's a useful function that'll let you feed in a ratio between -1 and 1 to any of the standard (non-configurable) eases to make them "weighted" in one direction or the other, as if it's pulling the ease curve toward the start or the end. A ratio of "0" won't be weighted either way, -1 would be weighted toward the "in" portion of the ease, and 1 is weighted toward the "out" portion.

function addWeightedEases() {
  let eases = gsap.parseEase(),
    createConfig = (ease) => (ratio) => {
      let y = 0.5 + ratio / 2;
      return (p) => ease(2 * (1 - p) * p * y + p * p);
    };
  for (let p in eases) {
    if (!eases[p].config) {
      eases[p].config = createConfig(eases[p]);
    }
  }
}

//example usage:
ease: "power2.inOut(0.5)"; // weighted halfway to the "out" portion
ease: "power2.inOut(-0.2)"; // weighted slightly to the "in" portion
ease: "power2.inOut(-1)"; // weighted ALL THE WAY to the "in" portion
ease: "power2.inOut(1)"; // weighted ALL THE WAY to the "out" portion

After you run that function once, you can basically configure any of the standard eases like power2.inOut or power1.in (or whatever) by adding parenthesis with a number indicating how you'd like to weight the ease in one direction or the other. And again, it works with any standard ease that doesn't already have a configuration option (like "steps()", "slow()", etc.)