将字符串转换为 spinal case。Spinal case 是 all-lowercase-words-joined-by-dashes 这种形式的，也就是以连字符连接所有小写单词。

代码：

function spinalCase(str) {
  // "It's such a fine line between stupid, and clever."
  // --David St. Hubbins
  str = str.replace(/([A-Z]+)/g,' $1');
  str = str.replace(/\s+|_+/g,'-');
  if(str[0] == "-"){str = str.substring(1);}
  str = str.replace(/--/g,'-');
  str = str.toLowerCase();
  return str;
}

spinalCase("thisIsSpinalTap");