JavaScript Patterns 4.8 Function Properties - A Memoization Pattern

Gets a length property containing the number of arguments the function expects:

function func(a, b, c) {}

console.log(func.length); //

var myFunc = function () {

    //  serialize the arguments object as a JSON string and use that string as a key in your cache object

    var cachekey = JSON.stringify(Array.prototype.slice.call(arguments)),

    if (!myFunc.cache[cachekey]) {

        var result = {};

        // ... expensive operation ...

        myFunc.cache[cachekey] = result;

    }

    return myFunc.cache[cachekey];

};

// cache storage

myFunc.cache = {};

References: 

JavaScript Patterns - by Stoyan Stefanov (O`Reilly)