FCC Spinal Tap Case

function spinalCase(str) {
  // "It's such a fine line between stupid, and clever."
  // --David St. Hubbins
  str=str.replace(str.charAt(0),str.charAt(0).toLowerCase());//将字符串首字母小写化，做不处理
  var reg=/[\s|'_'|A-Z]/g;//正则匹配替换区
  var arr=str.match(reg);//提取对应的内容
  if(arr){//如果提取到了
    for(var i in arr){
     if(arr[i]==' '||arr[i]=='_') str=str.replace(arr[i],'-');
      else if(arr[i]>='A'&&arr[i]<='Z'&&arr[i-1]!=' '&&arr[i-1]!='_'){str=str.replace(arr[i],'-'+arr[i]);}
    }
  }

  return str.toLowerCase();
}

spinalCase('This Is Spinal Tap');