根据 x、y 位置计算角度。

我正试图根据箭头所要到达的位置计算箭头所需旋转的角度。箭头移动的方向非常复杂，有没有人可以指点一二？

可以在Codepen上查看代码： Codepen

我在这里添加了完整的代码（根据输入进行了编辑）

class Throwable {
  constructor(){
    this.throwObject = null;
    this.canDrag = null;
    this.initialDiffX = 0;
    this.initialDiffY = 0;
    this.previousX = 0;
    this.previousY = 0;
    this.intervalCounter = 0;
  }
  set x(input) {
    this.throwObject.style.left = input + 'px';
  }
  set y(input) {
    this.throwObject.style.top = input + 'px';
  }
  set rotation(input) {
    this.throwObject.style.transform = `rotate(${input}deg)`;
  }
  init(){
    this.throwObject = document.querySelector('.throwable');
    this.throwObject.addEventListener('mousedown', this.activateDrag.bind(this));
    this.throwObject.addEventListener('mouseup', this.deactivateDrag.bind(this));
    document.addEventListener('mousemove', this.drag.bind(this));
  }
  activateDrag(event) {
    this.canDrag = true;
    this.initialDiffX = event.clientX - this.throwObject.offsetLeft;
    this.initialDiffY = event.clientY - this.throwObject.offsetTop;
  }
  deactivateDrag() {
    this.canDrag = false;
  }
  drag(event) {
    if(this.canDrag === true) {
      if(this.intervalCounter >= 30) {
         this.intervalCounter = 0;
      }
      if(this.intervalCounter === 0) {
        this.previousX = event.clientX;
        this.previousY = event.clientY;
      }
      this.intervalCounter++;
      this.y = event.clientY- this.initialDiffY;
      this.x = event.clientX - this.initialDiffX;
      this.rotation = this.angle(event.clientX, event.clientY, this.previousX, this.previousY);
    }
  }
  angle(ex, ey, cx, cy) {
    var dy = ey - cy;
    var dx = ex - cx;
    return Math.atan2(dy, dx) * 180 / Math.PI + 90;
  }
  // Untility
  log(logObject) {
    let logStr = '';
    for(let key in logObject) {
      logStr += `${key}: ${logObject[key]}
`;
    }
    document.getElementById('log').innerHTML = logStr;
  }
}
let throwable = new Throwable();
throwable.init();

我在比较两个不同值时犯了一个错误，我已经修复了它，现在它效果比之前好多了，只是有时候还有些奇怪的行为，好像不知道在某些点上该往哪里走。不过总体来说还是比之前好多了。