【javascript】将16进制颜色或者rgb转换成rgba

/***
 * //将16进制颜色或者rdb转换成rgba
 * @param color
 * @param opacity
 * @returns {string}
 */
function hex2rgb(color,opacity=1)=>{
  if(/^(rgb|RGB)/.test(color)){
    let arr  = color.toString().split(',');
    arr[3]= opacity+')';
    return arr.join(',');
  }
  color=color.substring(1);
  color=color.toLowerCase();
  let b= [];
  for(let i=0;i<3;i++){
    b[0]=color.substr(i*2,2);
    b[3]="0123456789abcdef";
    b[1]=b[0].substr(0,1);
    b[2]=b[0].substr(1,1);
    b[20+i]=b[3].indexOf(b[1])*16+b[3].indexOf(b[2]);
  }
  return "rgb(" +b[20]+","+b[21]+","+b[22]+ ","+opacity+")";
}