function cached(fn) {
var cache = Object.create(null);
return (function cachedFn(str) {
var hit = cache[str];
return hit || (cache[str] = fn(str))
})
}
var capitalize = cached(function (str) {
return str.charAt(0).toUpperCase() + str.slice(1)
});
capitalize('aaaa') // Aaaa
