Maybe monad in JS

maybe.js

// Requires testers.js for existy() and isRealNaN()
/**
 * Maybe Monad (chainable, failure tolerant)
 * 
 * Maybe(value, failOn).bind(function(value) { return value * value; }).value()
 */

var Maybe = function Maybe(val) {
  if (!(this instanceof Maybe)) {
		return new Maybe(val);
	}

	this.value = val;
};
	
Maybe.unit = function unit(value) {
	return new Maybe(value);
};

Maybe.fnBind = function fnBind(fn) {
	return function() {
		return fn(arguments[0].value);
	};
};

Maybe.prototype.mBind = function mBind(fn) {
	return Maybe.unit(existy(this.value) ? fn(this.value) : null);
};