stync

Ever have this happen? You've got a bunch of asynchronous code that includes calls to console.log (or process.stdout.write); and it gets all jumbled because your callbacks fire in non-deterministic order.

This is just a little library to make things a bit more orderly.

Usage

var async = require('async'),
    http  = require('http'),
    stync = require('stync');
 
var urls = [
  "http://www.google.com",
  "http://www.yahoo.com",
  "http://www.amazon.com",
  "http://www.stackoverflow.com",
  "http://www.reddit.com",
  "http://www.github.com",
  "invalid URL"
];
 
async.each(urls, function(url) {
  // stync.begin indicates you're starting a new line in your output;
  // it returns a message object that you can use to continue writing
  // to the same line. Subsequent messages are queued up so that they will not
  // print until this message is finished.
  var message = stync.begin('Fetching "' + url + '"...');
 
  var request = http.get(url, function(response) {
    // message.write adds more text to the current line, without progressing to
    // the next message in the queue.
    message.write(' received response (' + response.statusCode + ')...');
 
    var bytesReceived = 0;
 
    response.on('data', function(data) {
      bytesReceived += data.length;
    });
 
    response.on('end', function(data) {
      // message.end terminates the current line. Any subsequent lines (that you
      // started w/ stync.begin) will now be written, when ready, in the order
      // in which they were enqueued.
      message.end(' read ' + bytesReceived + ' bytes');
    });
  });
 
  request.on('error', function(err) {
    message.end(' ' + err);
  });
});
 

In the above example, all URLs are requested in parallel. Suppose a response is received from the last URL first. Everything will still display properly because each message does not write itself to process.stdout until its predecessor has called end. In effect, messages "wait their turn" so that line-by-line the console output makes sense:

Fetching "http://www.google.com"... received response (200)... read 44887 bytes
Fetching "http://www.yahoo.com"... received response (200)... read 92645 bytes
Fetching "http://www.amazon.com"... received response (200)... read 170218 bytes
Fetching "http://www.stackoverflow.com"... received response (301)... read 148 bytes
Fetching "http://www.reddit.com"... received response (200)... read 111658 bytes
Fetching "http://www.github.com"... received response (301)... read 0 bytes
Fetching "invalid URL"... Error: connect ECONNREFUSED