DateMathParser for JavaScript

datemathparser.js

  var DateMathParser = function() {

    return {
      parse: function(match) {
        var dt = new moment();
        if (0 == match.length) {
          return dt;
        };
        var splitter = new RegExp("([^/]*)([/]{0,1})([^\\-\\+]*)(.*)");
        var pos = 0;
        var ops = _.reject(match.split(splitter), function(d) { return !d; });

        // check if first ops is NOW or DATE
        var date = ops.shift();
        if (date != 'NOW') {
          dt = new moment(date);
        }

        while (pos < ops.length) {
          var txt = ops[pos++];
          var command = txt.charAt(0);
          switch (command) {
            case 'N':
              // someone provided 'NOW'
              break;
            case '/':
              // rounding date down (using moment)
              dt = dt.startOf(ops[pos++].toLowerCase());
              break;
            case '+': // fall through
            case '-':
              // extract date math adn apply to current dt
              var terms = _.reject(txt.split(new RegExp("([\\-\\+]+)([0-9]+)(.+)")), function(d) { return !d });
              var plus_or_minus = terms[0];
              var numeric = terms[1];
              var part = terms[2];

              switch (part) {
                case 'DAYS':
                  part = 'DAY';
                  break;
                case 'HOURS':
                  part = 'HOUR';
                  break;
                case 'WEEKS':
                  part = 'WEEK';
                  break;
                case 'MINUTES':
                  part = 'MINUTE';
                  break;
                case 'SECONDS':
                  part = 'SECOND';
                  break;
                case 'MILLISECONDS':
                  part = 'MILLISECOND';
                  break;
                case 'MONTHS':
                  part = 'MONTH';
                  break;
                case 'YEARS':
                  part = 'YEAR';
                  break;
              }

              if (plus_or_minus == '-') {
                dt = dt.subtract(part.toLowerCase(), numeric); 
              } else {
                dt = dt.add(part.toLowerCase(), numeric); 
              }

              break;
            default:
              throw 'Not parsable';
          }
        }

        return dt;
      }
    }
  };
  
  // usage
  var parser = new DateMathParser();
  console.log(parser.parse('NOW/DAY')); // does today rounded to 00:00:00
  console.log(parser.parse('NOW/MONTH')); // does today rounded to nearest month @ 00:00:00
  console.log(parser.parse('NOW/WEEK')); // does today rounded to nearest month @ 00:00:00
  console.log(parser.parse('NOW/YEAR')); // does today rounded to nearest month @ 00:00:00
  
  console.log(parser.parse('NOW/DAY+5DAYS')); // does today rounded to nearest day and adds 5 days
  console.log(parser.parse('NOW/DAY-5DAYS')); // does today rounded to nearest day and subtracts 5 days
  console.log(parser.parse('NOW/DAY+1MONTH')); // does today rounded to nearest day and adds 1 month
  console.log(parser.parse('NOW/DAY-1MONTH')); // does today rounded to nearest day and subtracts 1 month
  
  console.log(parser.parse('NOW+1HOUR')); // right now to the second and adds 1 hour
  console.log(parser.parse('NOW-1HOUR')); // right now to the second and subtracts 1 hour
  
  console.log(parser.parse('2013-06-28T00:00:00Z+1DAY')); // 1 DAY plus the specified time

Borrows from http://lucene.apache.org/solr/4_9_0/solr-core/org/apache/solr/util/DateMathParser.html