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Queue.js is yet another asynchronous helper library for JavaScript. Think of it as a minimalist version of Async.js that allows fine-tuning over parallelism. Or, think of it as a version of TameJs that does not use code generation.

For example, if you wanted to stat two files in parallel:

    .defer(fs.stat, __dirname + "/../Makefile")
    .defer(fs.stat, __dirname + "/../package.json")
    .await(function(error, results) { console.log(results); });

Or, if you wanted to run a bazillion asynchronous tasks (here represented as an array of closures) serially:

var q = queue(1);
tasks.forEach(function(t) { q.defer(t); });
q.await(function(error, results) { console.log("all done!"); });

Queue.js can be run inside Node.js or in a browser.

API Reference


Constructs a new queue with the specified parallelism. If parallelism is not specified, the queue has infinite parallelism. Otherwise, parallelism is a positive integer. For example, if parallelism is 1, then all tasks will be run in series. If parallelism is 3, then at most three tasks will be allowed to proceed concurrently; this is useful, for example, when loading resources in a web browser.

queue.defer(method[, arguments…])

Adds the specified method to the queue, with any optional arguments. The method is called with the optional arguments and a final callback argument, which should be called when the task has finished.


Sets the callback to be notified when all deferred tasks have finished.


The callbacks follow the Node.js convention where the first argument is an optional error object, and the second is used to pass on the result of an operation.