Convert a string to spinal case. Spinal case is all-lowercase-words-joined-by-dashes.

spinal-tap-case.js

function spinalCase(str) {
  // "It's such a fine line between stupid, and clever."
  // --David St. Hubbins
  function processStr(match, offset, string){
    //if the offset is not the first letter and there isn't already a hyphen, 
    //add a hyphen then change the letter to lowercase
    if(offset !== 0 && string[offset-1] !== '-'){
      return '-' + match.toLowerCase();
    }
    return match.toLowerCase();
  }
  //first check for spaces, then check for underscores, then check for capitals
  var newStr = str.replace(/\s/g, '-').replace(/_/g, '-').replace(/[A-Z]/g, processStr);
  
  return newStr;
}

spinalCase('This Is Spinal Tap');