export interface IconProps {
  type: string;
  className?: string;
  title?: string;
  onClick?: React.MouseEventHandler<any>;
  spin?: boolean;
  style?: React.CSSProperties;
}

const Icon = (props: IconProps) => {
  const {type, className = "", spin} = props;

  const classString = classNames({
    anticon: true,
    "anticon-spin": !!spin || type === "loading",
    [`anticon-${type}`]: true,
  }, className);
  return <i {...omit(props, ["type", "spin"])} className={classString}/>;
};

export default Icon;

this is the simplest Icon component source code, see! spin here. I don"t understand why I use spin to write like this. At first, I thought that if spin is not passed in, then this value is undefined, so we need to use! undefined to convert to boolean type, but later I tested that undefined defaults to false, which does not seem to affect the result. I hope someone can solve the problem.
because it is written like this in many other components