Asynchronous Programming: High Level Primitives

With the advent of the Twisted asynchronous framework, the concept of a continuous result has become very popular.

First of all, I recommend reading the articles: Asynchronous programming: the concept of Deferred , Deffered for JavaScript .

But using delayed results is not very convenient without higher-level abstractions. And now we have the Do framework  .

Now we can perform such actions:

Perform multiple actions in parallel

// Multiple arguments
Do.parallel(
  Do.read("/etc/passwd"),
  Do.read(__filename)
)(function (passwd, self) {
  // Do something
}, error_handler);

// Single argument
var actions = [
  Do.read("/etc/passwd"),
  Do.read("__filename")
];
Do.parallel(actions)(function (results) {
  // Do something
}, error_handler);

Perform several actions in sequence

// Multiple arguments
Do.chain(
  Do.read(__filename),
  function (text) {
    return Do.save("newfile", text);
  },
  function () {
    return Do.stat("newfile");
  }
)(function (stat) {
  // Do something
}, error_handler);

// Single argument
var actions = [
  Do.read(__filename),
  function (text) {
    return Do.save("newfile", text);
  },
  function () {
    return Do.stat("newfile");
  }
];
Do.chain(actions)(function (stat) {
  // Do something
}, error_handler);

Map source array to resultant asynchronously

var files = ['users.json', 'pages.json', 'products.json'];
function load_file(filename, callback, errback) {
  fs.read(filename)(function (data) {
    callback([filename, data]);
  }, errback);
}
Do.map(files, load_file)(function (contents) {
  // Do something
}, error_handler);

Filter array asynchronously

var files = ['users.json', 'pages.json', 'products.json'];
function is_file(filename, callback, errback) {
  fs.stat(filename)(function (stat) {
    callback(stat.isFile());
  }, errback);
}
Do.filter(files, is_file)(function (filtered_files) {
  // Do something
}, error_handler);

In addition, wrappers for node.js are provided  . Project on github .