Partial application of a function

gistfile1.js

/**
 * Returns a new function that invokes `func` in a specified context and
 * with specified set of arguments.
 * The arguments to this function serve as a template.  Undefined values
 * in the argument list are filled in with values from the inner set.
 *
 * Example: var f = function(x, y, z) { return x * (y - z); }
 *          partialApply(f, undefined, 2)(3, 4) // => -6: 3 * (2 - 4)
 * 
 * @param func {Function} A function to invoke.
 * @return {Function} A new function with partially applied arguments.
 */
function partialApply(func /* , ... */) {
    var outerArgs = arguments;  // Save the outer arguments array
    return function() {
        var args = array(outerArgs, 1);  // Start with an array of outer args
        var i = 0, j = 0, len = args.length;
        // Loop through those args, filling in undefined values from inner
        for (; i < len; i++)
            if (args[i] === undefined) args[i] = arguments[j++];
        // Now append any remaining inner arguments
        args = args.concat(array(arguments, j));
        return func.apply(this, args);
    };
}