cache.js

var buildKeySus = function (patternObj, data) {
  var pattern = patternObj.pattern
  var duration = patternObj.duration || DEFAULT_CACHE_AGE_MS
  data = data || {}

  var patternParts = pattern.split('/')
  var key = ''

  for (var i = 0; i < patternParts.length; i++) {
    if (patternParts[i].charAt(0) === ':') {
      var dataKey = patternParts[i].substr(1)
      // if a pattern-matched portion of the key is missing, exit out
      // of the key building with the currently built portion of the key.
      // e.g. the key /collectionPosts/:collectionId/:postId with
      // {collectionId: 123} would return /collectionPosts/123/
      if (!data[dataKey]) return {
        key: key,
        duration: duration
      }
      key += data[dataKey] || 'null'
    } else {
      key += patternParts[i]
    }

    if (i < patternParts.length - 1) key += '/'
  }

  return {
    key: key,
    duration: duration
  }
}

var buildKeyLegit = function (patternObj, data) {
  return {
    key: keyBuilder(patternObj.pattern)(data || {}),
    duration: patternObj.duration || DEFAULT_CACHE_AGE_MS
  }
}

function keyBuilder(key) {
  for (var parts = key.split('/'),  _=(parts[0] == "" && parts.shift()), l = parts.length, fA = '(function(data) {\n\treturn \"/', i = 0; i < l; i++) {
    fA += (parts[i][0] == ':' ? "\"+(var s = data[\'" + parts[i].slice(1) + "\'] ? data[\'" + parts[i].slice(1) + "\'] + '/' : '')+\"" : parts[i] + '/')
  }
  return eval(fA + '\"\n})', {})
}

// console.log(keyBuilder('/collection/:controller/:action/:id'))
console.log(keyBuilder('/collection/:controller/:action/:id')({controller: 'foo', action: 'bar', id: '123'}))
console.log(keyBuilder('/collection/:controller/:action/:id')({controller: 'foo'}))



console.log('old', buildKeySus({pattern: '/b/:controller/:action/:id', duration: 60}, {controller: 'foo', action: 'bar', id: '123'}))
// old { key: '/b/foo/bar/123', duration: 60 }
console.log('new', buildKeyLegit({pattern: '/b/:controller/:action/:id', duration: 60}, {controller: 'foo', action: 'bar', id: '123'}))
// new { key: '/b/foo/bar/123', duration: 60 }
console.log('mod', buildKeyLegit({pattern: '/b/:controller/:action/:id', duration: 60}, {controller: 'foo', id: '123'}))
// mod { key: '/b/foo/123', duration: 60 }
console.log('mod', buildKeyLegit({pattern: '/b/:controller/:action/:id', duration: 60}, {}))
// mod { key: '/b', duration: 60 }