Demonstrate non-intuitive `async.waterfall` behavior.

async_error.js

var async = require("async");

function asyncExample (callback) {
    console.log("asynchronous error");
    async.waterfall(
        [
            function (next) {
                console.log("throwing error");
                next(new Error("Fail!"));
            },
            function (next) {
                console.log("after error");
                next();
            }
        ],
        function (error) {
            console.log("final handler");
            console.log(error);
            callback();
        }
    );
}

function syncExample () {
    console.log("synchronous error");
    async.waterfall(
        [
            function (next) {
                console.log("throwing error");
                // Synchronous errors bubble up the stack and interrupt execution (meaning that `next` is
                // never called).
                throw new Error("Fail!");
                next();
            },
            function (next) {
                console.log("after error");
                next();
            }
        ],
        function (error) {
            // This never executes because the default exception handler will terminate execution if there
            // is an unhandled exception.
            console.log("final handler");
            console.log(error);
        }
    );
}

asyncExample(syncExample);