// these are your keyframes, in a format compatible with THREE.Vector3.
// Please note that the time `t` is expected in milliseconds here.
// (must have properties named x, y and z - otherwise the copy below doesn't work)
const keyframes = [
  {t: 0, x: 318, y: 24, z: 3},
  {t: 25, x: 318, y: 24, z: 3},
  // ... and so on
];

// find a pair of keyframes [a, b] such that `a.t < t` and `b.t > t`.
// In other words, find the previous and next keyframe given the
// specific time `t`. If no previous or next keyframes is found, null
// is returned instead.
function findNearestKeyframes(t) {
  let prevKeyframe = null;
  for (let i = 0; i < keyframes.length; i++) {
    if (keyframes[i].t > t) {
      return [prevKeyframe, keyframes[i]];
    }
    prevKeyframe = keyframes[i];
  }

  return [prevKeyframe, null];
}

const tmpV3 = new THREE.Vector3();

function loop(t) {
  const [prevKeyframe, nextKeyframe] = findNearestKeyframes(t);

  // (...not handling cases where there is no prev or next here)

  // compute the progress of time between the two keyframes
  // (0 when t === prevKeyframe.t and 1 when t === nextKeyframe.t)
  let progress = (t - prevKeyframe.t) / (nextKeyframe.t - prevKeyframe.t);

  // copy position from previous keyframe, and interpolate towards the
  // next keyframe linearly
  tmpV3.copy(nextKeyframe);
  someObject.position
    .copy(prevKeyframe)
    .lerp(tmpV3, progress);

  // (...render scene)

  requestAnimationFrame(loop);
}

// start the animation-loop
requestAnimationFrame(loop);