Make node.js code pretty via a generator-based library

The JavaScript server environment node.js has an intriguing approach to coding: Do other things while waiting for results from, say, a database. But don’t use threads to juggle those things, use continuations. This is similar to what client-side JavaScript code (such as Ajax calls) already looks like. Not having to create threads saves a lot of overhead when loads are high. Multi-core and multi-processor systems can still be supported, by scheduling one “instance” of node.js per core/processor.

The only problem with node.js code: You get one nested function expression for each outside request you make.

    io.doFirst(param1, function(foo) {
        io.doSecond(param2, function(bar) {
            // work with foo and bar
        });
    });

It is obvious that this can quickly turn ugly. Now David Herman from Mozilla has created jsTask [1], a JavaScript library that turns the above code into the much more readable code below [2].

    var foo = yield io.doFirst(param1);
    var bar = yield io.doSecond(param2);
    // work with foo and bar

This is reminiscent of multi-threading and blocking, but it works cooperatively (no preemptive multi-tasking). The similarities don’t end there: You can also do fork-join as follows:

    var [foo, bar] = yield join(io.doFirst(param1),
                                  io.doSecond(param2));

That way, you can perform both operations in parallel, but still only continue after both have finished. The library is based on generators [3], a JavaScript feature that is already in Firefox and might make it into the next version of the ECMAScript standard [4].

1. jsTask on GitHub
2. Who says JavaScript I/O has to be ugly?
3. Iterators and generators [Firefox documentation]
4. David Herman on ECMAScript.next

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Make node.js code pretty via a generator-based library