jsonStringToDate.js

var R_ISO8061_STR = /^(\d{4})-?(\d\d)-?(\d\d)(?:T(\d\d)(?:\:?(\d\d)(?:\:?(\d\d)(?:\.(\d{3}))?)?)?(Z|([+-])(\d\d):?(\d\d)))?$/;

function jsonStringToDate(string) {
  var match;
  if (match = string.match(R_ISO8061_STR)) {
    var date = new Date(0),
        tzHour = 0,
        tzMin = 0;
    if (match[9]) {
      tzHour = int(match[9] + match[10]);
      tzMin = int(match[9] + match[11]);
    }
    date.setUTCFullYear(int(match[1]), int(match[2]) - 1, int(match[3]));
    date.setUTCHours(int(match[4] || 0) - tzHour,
        int(match[5] || 0) - tzMin,
        int(match[6] || 0),
        int(match[7] || 0));
    return date;
  }
  return string;
}

function int(str) {
  return parseInt(str, 10);
}