A simple example

[jonasseglare]

Hi,

I just want to contribute with a simple example in case you are interested:

// Compile this file with
//
// _node -c hello._js
//
// or run it directly with
//
// _node hello._js

// Recursive implementation
function factorial(n, _) {
    if (n < 0) {

    // Is this the proper way to produce an error?
    throw new Error('An error');

    } else {
    if (n == 0) {
        return 1; // <-- will result int callback being called.
    } else {
        var subresult = factorial(n-1, _);
        return n*subresult; // <-- will result in callback being called.
    }
    }
}

// Delivers the result by calling a callback.
function multiply(a, b, _) {

    // This return statement will produce a callback.
    return a*b;
}

// Iterative implementation
function factorial2(n, _) {
    var result = 1;

    // Iterations with callbacks also work :-)
    for (var i = 1; i <= n; i++) {

    // Call to callback-style multiply.
    result = multiply(result, i, _);
    }

    // Will call the callback.
    return result;
}

// Non-callback-based factorial
function factorial3(n) {
    if (n == 0) {
    return 1;
    } else {
    return n*factorial3(n - 1);
    }
}

var x = 9;
var y = factorial(x, _);
var y2 = factorial2(x, _);
var y3 = factorial3(x);

// Please note that all y's will be evaluated before we reach this point :-)
console.log('Factorial of ' + x + ' is ' + y + ' or ' + y2 + ' or ' + y3);




///////////////////////////////////// INVESTIGATE STRATEGIES FOR ERROR HANDLING
var errorHandling = 'traditional'

if (errorHandling == 'none') { 
    console.log('Calling factorial with a negative number, NO ERROR HANDLING: ', factorial(-30, _));
} else if (errorHandling == 'traditional') {
    factorial(
        -30,
    function(err, value) {
        console.log('Calling factorial with a negative number, WITH ERROR HANDLING: ');
        console.log('err = ', err);
        console.log('value = ', value);
    }
    );
} else {
    try {
    console.log('Calling factorial with a negative number, IN TRY STATEMENT: ', factorial(-30, _));
    } catch (e) {
    console.log('Exception caught trying to evaluate factorial with negative number');
    }
}