An idea for parsing arguments in Meteor.js With this code declaring interfaces and validating input just got a bit easier..

argumentparser.js

typeNames = function(type) {
  if (Match.test(type, [Match.Any])) return 'array';
  if (type === Object) return 'object';
  if (type === String) return 'string';
  if (type === Number) return 'number';
  if (type === Boolean) return 'boolean';
  if (type === Function) return 'function';
  return typeof type;
};

// If arguments are correctly parsed then return the object
// otherwice we return the new Error() object - the user can then throw this
// if relevant
parseArguments = function(args, names, types) {
  // Names are array of strings or string in array
  check(names, [Match.OneOf(String, [String])]);
  check(types, [Match.Any]);
  check(args, [Match.Any]);
  // Check lengths, we throw this since this function needs this
  if (names.length !== types.length) {
    throw new RangeError('names and types dont match');
  }
  // Make sure we dont have too many arguments to begin with, return parse error
  if (args.length > names.length) {
    return new Error('too many arguments');
  }
  var requiredLength = 0;
  // Count required arguments
  for (var i = 0; i < names.length; i++) {
    if (names[i] === ''+names[i]) {
      requiredLength++;
    }
  }
  // Make sure we have enough arguments
  if (args.length < requiredLength) {
    return new Error('not enough arguments');
  }

  // The returning result object
  var result = {};
  // Argument index
  var a = 0;
  // Init number of allowed optionals left
  var optionalsLeft =  args.length - requiredLength;
  // Go find a match
  for (var i = 0; i < types.length; i++) {
    // If name is a string then argument is required
    var isRequired = names[i] === ''+names[i];
    var name = (isRequired)? names[i] : names[i][0];
    // Check to see if we have a type match
    if (Match.test(args[a], types[i])) {
      if (isRequired || optionalsLeft > 0) {
        // If not required then decrease number of optionals left
        isRequired || optionalsLeft--;
        // Check if we are about to overwrite an existing key
        if (typeof result[name] !== 'undefined') {
          throw new Error('duplicate argument names "' + name + '"');
        }
        // Set key and value on result
        result[name] = args[a]; // could use args[a++]
        // Goto next argument
        a++;
      }
    } else {
      // We are not allowed to skip over isRequired arguments
      if (isRequired) {
        return new TypeError('type (' + typeNames(args[a]) +
                ') did not match (' + typeNames(types[i]) +
                ') for required argument "' + names[i] + '"');
      } // If not isRequired we skip to the next
      // If more arguments left than interface allows then we are
      // out of bounds...
      if (args.length - a > types.length - i) {
        return new TypeError('type (' + typeNames(args[a]) +
                ') did not match remaining arguments.' +
                ' eg.: "' + names[i-1] + '" (' + typeNames(types[i-1]) + ')');
      }
    }
  }

  return result;
};

test.js

Test = function(/* name, [options], [nr], nr2, [on], callback */) {
  var self = this;
  var result = parseArguments(arguments,
    ['name', ['options'], ['nr'],  'nr2', ['on'], 'callback' ],
    [String,    Object,   Number,  Number, Boolean,  Function]
  );

  var self.options = {
    test: 'default'
  };

  // If the parseArgument returned an instance of Error we can
  // throw it or test with another parseArguments if we also
  // accept a complete different input pattern
  if (result instanceof Error) {
    throw result;
  } else {
    // Finally the user got it right, we can now trust the
    // input
    console.log('GOT:');
    console.log(result);
    // Extend and overwrite options - we could use a more
    // specific match than using Object
    _.extend(self.options, result.options || {});
    // Maybe use the callback
    result.callback('We do have a callback since its required');
  }
};

Here are some tests I did with it:

var at = function(/* name, [options], [nr], nr2, [on], callback */) {
  var result = parseArguments(arguments,
            ['name', ['options'], ['nr'], 'nr2', ['on'], 'callback'],
            [String, Object, Number, Number, Boolean, Function]
            );

  // If the parseArgument returned an instance of Error we can
  // throw it or test with another parseArguments if we also
  // accept a complete different input pattern
  if (result instanceof Error) {
    console.log(result.message);
  } else {
    console.log('GOT:', result);
  }
};

at();
at(function() {});
at("myName", 200);
at("myName", {});
at("myName", 200, function() {});
at("myName", {}, 200, function() {});
at("myName", {}, 100, 200, function() {});
at("myName", 100, 200, function() {});
at("myName", 100, 200, true, function() {});
at("myName", 100, 200, "true", function() {});
at("myName", {}, 100, 200, true, function() {});
at("myName", null, null, 200, null, function() {});
at("myName", void 0, void 0, 200, void 0, function() {});
at("myName", 200, true, function() {});

Thanks, nice :) yeah null is a bitch