async-promise

This library provides Javascript-like promises to Ruby. It allows you to create and manage asynchronous operations with ease, providing a familiar API for those who have worked with JavaScript promises.

This library provides a Ruby implementation of ES6-like JavaScript Promises. It allows one to build asynchronous logic with ease, in addition to being able to handle exceptions. Under the hood, this library uses the async gem for concurrency management.

Install the gem via bundler by executing:

bundle add async-promise

Here's how to create a new promise and resolve it with the value "Success!". By calling the then method on our promise, we get to hook additional tasks that should be carried out after the promise is settled. The first lambda argument in the then method specifies the action to take if promise was resolved successfully. The second lambda argument specifies the action to take if the promise was rejected.

require "async"
require "async/promise"

Async do
  promise = Async::Promise.new()

  promise
    .then(->(value) { puts "Resolved with: #{value}" }) # callback for success
    .catch(->(reason) { puts "Error: #{reason}" })      # callback for failure

  promise.resolve("Success!")
  # console output:
  # Resolved with: Success!
end

This example demonstrates how to chain multiple then calls, passing the resolved value along the chain.

require "async"
require "async/promise"

Async do
  promise = Async::Promise.new()

  promise
    .then(->(value) { return "#{value} World" }) # Modify the value
    .then(->(value) { return "#{value}!" })      # Further modify the value
    .then(->(value) { puts value })              # Output the final value

  promise.resolve("Hello")
  # console output:
  # Hello World!
end

This example demonstrates how to handle promise rejections by using the catch method, or using the second argument of the then method.

require "async"
require "async/promise"

Async do
  promise1 = Async::Promise.new()

  promise2 = promise1
    .then(->(value) { puts "Resolved with: #{value}" }) # This won't be called
    .catch(->(reason) {
      puts "Caught error: #{reason}"
      raise "Error when catching error!?"
    }) # Error handling in addition to throwing another error, which is caught in the next `then` promise.
    .then(
      nil,
      ->(reason) {
        puts "Caught yet another error: #{reason}"
        return "hEy b0ss!"
      }
    )

  promise1.reject("Something went wrong!")
  # console output:
  # Caught error: Something went wrong!
  # Caught yet another error: Error when catching error!?

  puts promise2.wait # wait for the promise to get its resolved value
  # console output:
  # hEy b0ss!

  # waiting for a rejected promise will raise an error
  begin puts promise1.wait # an error will be raised here
  rescue => error; puts error.message
  end
  # console output:
  # Something went wrong!
end

Check out the type annotations and YARD doc comments in the ./sig/async/promise.rbs file. Otherwise, a summary follows:

• #status(): Returns the current status of the promise: "pending", "fulfilled", or "rejected".
• #resolve(value): Fulfills the promise with the given value.
• #reject(reason): Rejects the promise with the provided reason.
• #then(on_resolve, on_reject): Chains asynchronous operations and provides handlers for resolution and rejection.
• #catch(on_reject): Catches errors that occurred in preceding promise chains.
• #wait: Blocks the current execution until the promise is settled and returns the resolved value or raises an error if rejected.

• .resolve(value): Creates a pre-resolved promise.
• .reject(reason): Creates a pre-rejected promise.
• .all(promises): Returns a promise that resolves when all input promises are resolved or rejects when any one of them is rejected.
• .race(promises): Returns a promise that settles as soon as any input promise is settled (either fulfilled or rejected).
• .timeout(resolve_in, reject_in, resolve, reject): Returns a promise that settles after a specified timeout, either resolving or rejecting.

Bug reports and pull requests are welcome on GitHub at: https://github.com/omar-azmi/async-promise-ruby.

Clone the repo

git clone https://github.com/omar-azmi/async-promise-ruby.git

Install dependencies

bundle install

Run tests (in parallel)

bundle exec sus-parallel

Make changes to the source code and increment the library version.

Build the gem library file

gem build "./async-promise.gemspec"

Push the changes to rubygems.org

gem push "./async-promise-*.gem"