SPD (speed) determines who goes first, and the amount of actions that can be made in a turn. Here, the example uses two speeds: [125, 100]. The higher the value the faster. 125 can make 2 actions on every 4th turn, or 1.25 actions every turn to put it simply.

speed.js

function actions_per_turn(speeds, turns) {
  const arr = [];
  const slowest_speed = Math.min(...speeds);
  for (const speed of speeds) {
    const speed_arr = [];
    let remainder = 0;
    for (let i = 0; i < turns; i++) {
      const value = speed / slowest_speed + remainder;
      const floored = Math.floor(value);
      speed_arr.push(floored);
      remainder = value - floored;
    }
    arr.push(speed_arr);
  }
  return arr;
}

const arr = actions_per_turn([125, 100], 10);
console.log(arr);