js-design-monads

function Identity(value) {
    this.value = value;
}
​
Identity.prototype.bind = function(transform) {
    return transform(this.value);
};
​
Identity.prototype.toString = function() {
    return 'Identity(' + this.value + ')';

参考

JavaScriptのモナド
http://postd.cc/monads-in-javascript/