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A fluent Javascript DSL for parsing the arguments object. Allows for simple, concise optional arguments and repeating numbers of arguments.

Replace your if-else statements today!


var updateOrder = function() {
  var args = parseArgs(arguments)
              .optional('discountCode', -1, {type: 'number'})
              .optional('referrer', null, {instance: User})
    'Name: ' + + ', discount code: ' + args.discountCode +
    ', referrer: ' + args.referrer + ', address: ' + args.address


To start the chain, call parseArgs(arguments), with the arguments keyword literally being passed into the function. You can then continue the chain with the following methods:

  • required(name), where name is the name of the argument.
  • optional(name, defaultValue, checker), where name is the name of the argument, defaultValue is a default value to assign to the argument if nothing gets passed in, and check is either an object with a type or instance field or a function. If check is an object, the optional argument will have its type checked against the string set in the type field (if provided), and check whether it's an instance of the class set in the instance field (if provided). If it's a function, the function should be of the form function(arg, index, args), where arg is the current argument being checked, index is the index of that argument in the total number of arguments, and args the argument object provided as an Array. If the function returns true, the argument will be considered to have been passed in and the default value will not be set; if it returns false, the default value will be set.
  • many(name, checker), where name is the name of the argument, and checker is the same as the checker above. Stores the passed-in values in an array; if none are passed in, the array will be empty.

Once the chain is done, just access the chain's end property to finish it off. The parsed arguments will be stored in the returned object using the names given to each of the argument parsing calls.