<!doctype html>

<html lang="en">

<head>

<title>JavaScript Patterns</title>

<meta charset="utf-8">

</head>

<body>

<script>

/* 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

</script>

</body>

</html>