JS partial-application

/* Title: Partial application
   Description: the process of fixing a number of arguments to a function, 
   producing another function of smaller arity
*/

var partialAny = (function(aps) {

    // This function will be returned as a result of the immediately 
    // invoked function expression and assigned to the `partialAny` var.
    function func(fn) {
        var argsOrig = aps.call(arguments, 1);
        return function() {
            var args = [],
            argsPartial = aps.call(arguments),
            i = 0;
            // Iterate over all the originally-spedicified arguments. If that
            // argument was the `partialAny._` placeholder, use the next just
            // passed-in argument, otherwise use the originally-specified 
            // argument.
            for (; i < argsOrig.length; i++) {
                args[i] = argsOrig[i] === func._ ? argsPartial.shift() : argsOrig[i];
            }

            // If any just-passed-in arguments remain, add them to the end.
            return fn.apply(this, args.concat(argsPartial));
        };
    }

    // This is used as the placeholder argument.
    func._ = {};

    return func;
})(Array.prototype.slice);

// Slightly more legitimate example
function hex(r, g, b) {
    return '#' + r + g + b;
}

var redMax = partialAny(hex, 'ff', partialAny._, partialAny._);
console.log(redMax('11', '22')); // "#ff1122"
// Because `_` is easier on the eyes than `partialAny._`, let's use
// that instead. This is, of course, entirely optional, and the name
// could just as well be `foo` or `PLACEHOLDER` instead of `_`.
var __ = partialAny._;

var greenMax = partialAny(hex, __, 'ff');
console.log(greenMax('33', '44'));

var blueMax = partialAny(hex, __, __, 'ff');
console.log(blueMax('55', '66'));

var magentaMax = partialAny(hex, 'ff', __, 'ff');
console.log(magentaMax('77'));

// reference
// http://msdn.microsoft.com/en-us/magazine/gg575560.aspx

参考 : https://github.com/shichuan/javascript-patterns/blob/master/function-patterns/partial-application.html