async tasks

generator.js

function* files() {
    var results = [];
    for (var k = 0; k < files.length; ++k)
        results.push(yield files[k]);
    return results;
}

var iterator = files();
function process(iterator, sendValue) {
    var fileTask = iterator.next(sendValue);
    fs.readFile(fileTask, function(err, res) {
        if (err) iterator.throw(err);
        else process(iterator, res);
    });
}
process(iterator);