autocurry.js

//see: http://mksenzov.github.io/javascript/2014/01/18/autocurry-in-js.html

// We create a function autocurry
function autocurry(fn) {

    // Autocurry takes an ordinary function `fn` as an argument 
    // and wraps it into a `magic` function
    return function /* magic */ () {
        // Magic checks the amount of formal parameters fn has: fn.length
        // vs. how much paramters where passed to `magic`: arguments.length

        if (fn.length > arguments.length) {
            // If there is not enough parameters: let's build and return 
            // a curried version of fn
            var slice = Array.prototype.slice;
            var args = slice.apply(arguments);

            return function() {
                return fn.apply(null, args.concat(slice.apply(arguments)));
            };
        } 

        // Otherwise let's just aply fn to arguments of `magic` and move on
        return fn.apply(null, arguments);
    };
}

// Basic `add` function:
function add(a, b) {
    return a + b;
}

// Enable auto-curry:
var add = autocurry(add);

// Normal application
add(1, 2); // => 3

// Auto-currying:
var add1 = add(1)
typeof add1 // => [Function]
add1(24)    // => 25