Example of a function that can wrap any function to make it support partial application. Relies on fun.length returning the number of expected arguments (e.g. all arguments included in function definition, not variable/implied from arguments object).

curryable.js

/**
 ** Example for creating curryable functions
 **/

// Helper to splice together 2 arrays, like arr.concat() except elements in 'arr1' containig 'empty' 
// are first "filled" with elements from arr2. 
// e.g. splice(['a', undefined, 'b'], ['c', 'd', 'e'])  --> ['a', 'c', 'b', 'd', 'e']
var splice = function (arr1, arr2, empty) {
	var arr2_ = Array.prototype.slice.call(arr2, 0),  // so this works with arguments objects
	 		result = Array.prototype.slice.call(arr1, 0);
	for (var i = 0; i < result.length && arr2_.length > 0; ++i) {
		if(result[i] === empty) result[i] = arr2_.shift();
	}
	return result.concat(arr2_);
}

/// Wrap a function to allow partial application, optional specify argument value to mean argument 
/// is being skipped (to allow currying from the right) - defaults to using undefined.
var curryable = function(fn, maybeArgs) {
	var argValues = maybeArgs === undefined ? [] : maybeArgs,
			capturedContext = this;

	return function() {

		// Update argument values with those supplied in this call (perform partial application)
		newArgValues = splice(argValues, arguments, undefined);

		// Check if sufficient arguments are provided then call the function with correct context if so,
		// otherwise return wrapper again passing values that were supplied for partial application
		if(newArgValues.length === fn.length && newArgValues.indexOf(undefined) === -1) {
			return fn.apply(capturedContext, newArgValues);
		} 
		else {
			return curryable(fn, newArgValues);
		}
	};
};

// Export curryable (to test as node module)
if (module) module.exports = curryable; 


// Example of use
if (require && require.main === module) {
  
  var __ = undefined
  
  var adder = curryable( function(a, b, c) { 
  	return (a + b) * c; 
  });
  
  var add1 = adder(1);
  var add2 = adder(__, 2);
  
  console.log(adder(10, 20, 1));
  console.log(add1(100, 1));
  console.log(add2(200, 1));

  var double1 = add1(__, 2);
  console.log(double1(50));
}