Promised-IO is a cross-platform package for asynchronous promise-based IO. Promises provide a simple robust mechanism asynchronicity with separation of concerns by encapsulating eventual completion of an operation with side effect free callback registration separate from call invocation. Promised-IO provides cross-platform file, HTTP, and system interaction with promises for asynchronous operations.

Promised-IO also utilizes "lazy arrays" for progressively completed actions or for streaming of data. Lazy arrays provide all the standard iterative Array methods for receiving callbacks as actions are completed. Lazy arrays are utilized for progressive loading of files and HTTP responses.

Promised-IO is part of the Persevere project, and therefore is licensed under the AFL or BSD license. The Persevere project is administered under the Dojo foundation, and all contributions require a Dojo CLA.