更改每次循环迭代的参数

如何解决更改每次循环迭代的参数

尝试一个简单的循环动画，在 animejs 循环中为每次迭代更改其参数。此代码更改了变量值，但未应用它们。值通过迭代保持不变。我怎样才能做到这一点？

  let
    R = Math.floor((Math.random() * 255)),G = Math.floor((Math.random() * 255)),B = Math.floor((Math.random() * 255)),dur = Math.floor((Math.random() * 4000));

      anime({ // <------------------------------------- Anime JS function
        targets: '.element',color: `rgb(${R},${G},${B})`,// <----------- Values I would like to change on each iteration
        duration: dur,// <--------------------------- Values I would like to change on each iteration
        loop: true,easing: 'linear',loopComplete: function (anim) { // <----------- Loop iteration callback
          R = Math.floor((Math.random() * 255));
          G = Math.floor((Math.random() * 255));
          B = Math.floor((Math.random() * 255));
          dur = Math.floor((Math.random() * 2000));
          console.log(R + ',' + G + ',' + B); // <---- Checked. RGB values are changing on each iteration.
        },});

let
  R = Math.floor((Math.random() * 255)),dur = Math.floor((Math.random() * 4000));

anime({
  targets: '#square',duration: dur,loop: true,loopBegin: function (anim) {
    R = Math.floor((Math.random() * 255));
    G = Math.floor((Math.random() * 255));
    B = Math.floor((Math.random() * 255));
    dur = Math.floor((Math.random() * 2000));
    console.log(R + ',' + B);
  },});

#square {
    font-size: 100px
  }

<script src="https://cdn.jsdelivr.net/npm/animejs@3.2.1/lib/anime.min.js"></script>


<div id="square">square</div>