async.md

nbd/util/async

The async module is a utility function module. Like all othe utility function modules, it is itself a function that can be called.

The purpose of async is to provide a platform-independent way to make use of timers in JavaScript to start another callstack after the current one.

(callback)

callback()

Since JavaScript is primarily a single-threaded environment, execution of another callstack is kicked off with an event. The async module makes use of window.postMessage() where available in order to register an event as immediate as possible after the current callstack has completed. Failing window.postMessage(), async falls back to using setTimeout() in order to achieve nearly the same effect, but see caveats.

require(['nbd/util/async'], function(async) {
  async(function() {
    console.log('bar');
  });
  console.log('foo'); // Logs 'foo' then 'bar'
});

Since the callback handed to async is executed on a separate callstack guaranteed to be after the current one, one use of the async module is to collect all calls to a function, and then only call the function once, if it was called at all.

require(['nbd/util/async'], function(async) {
  function fnIface() {
    fnIface.count = fnIface.count || 0;
    if (++fnIface.count === 1) async(fnImpl);
  }

  function fnImpl() {
    fnIface.count = 0;
    /* actual implementation */
  }

  for (var i=0; i<100; ++i) {
    fnIface(); // Only runs fnImpl() once after the loop finishes
  }
});