These are my solutions to the "problems" chapter in Douglas Crockford's workshop entitled "Javascript the Good Parts" (http://www.pluralsight.com/courses/javascript-good-parts).

solutions.js

function identity(num) {
    return num;
}

function add(num1, num2) {
    return num1 + num2;
}

function mul(num1, num2) {
    return num1 * num2;
}

function identityf(num) {
    return function() {
        return num;
    };
}

function addf(num1) {
    return function(num2) {
        return num1 + num2;
    };
}

function applyf(fun) {
    return function(num1) {
        return function(num2) {
            return fun(num1, num2);
        };
    };
}

function curry(fun, num1) {
    return function(num2) {
        return fun(num1, num2);
    };
}

function methodize(func) {
    return function(num2) {
        return func(this, num2);
    };
}
Number.prototype.add = methodize(add);

function demethodize(func) {
    return function(num1, num2) {
        return func.call(num1, num2);
    };
}

function twice(func) {
    return function(num) {
        return func(num, num);
    };
}

var double = twice(add);

var square = twice(mul);

function composeu(func1, func2) {
    return function(num) {
        return func2(func1(num));
    };
}

function composeb(func1, func2) {
    return function(num1, num2, num3) {
        return func2(func1(num1, num2), num3);
    };
}

function once(func) {
    return function() {
        var f = func;
        func = null;
        return f.apply(this, arguments);
    };
}

function counterf(num) {
    return {
        inc: function() {
            num = num += 1;
            return num;
        },
        dec: function() {
            num = num -= 1;
            return num;
        }
    };
}

function revocable(func) {
    return {
        invoke: function() {
            return func.apply(this, arguments);
        },
        revoke: function() {
            func = null;
        }
    };
}