gistfile1.js

Function.prototype.and = function () {
    var predicates = Array.prototype.slice.call(arguments);
    predicates.unshift(this);
    return (function (value) {
        return predicates.every(function (predicate) {
            return predicate(value);
        })
    });
}

Function.prototype.or = function () {
    var predicates = Array.prototype.slice.call(arguments);
    predicates.unshift(this);
    return (function (value) {
        return predicates.some(function (predicate) {
            return predicate(value);
        })
    });
}

// Usage:

var isBoth  = isFoo.and(isBar),
    isOneof = isFoo.or(isBar);