outwatch/outwatch

---

outwatch/outwatch.json

{
  "createdAt": "2016-11-04T17:26:16Z",
  "defaultBranch": "master",
  "description": "The Functional and Reactive Web-Frontend Library for Scala.js",
  "fullName": "outwatch/outwatch",
  "homepage": "http://outwatch.github.io",
  "language": "Scala",
  "name": "outwatch",
  "pushedAt": "2025-04-10T17:47:27Z",
  "stargazersCount": 469,
  "topics": [
    "frp",
    "functional-programming",
    "reactive",
    "rx",
    "sbt",
    "scala",
    "scalajs",
    "virtualdom"
  ],
  "updatedAt": "2025-10-09T11:07:59Z",
  "url": "https://github.com/outwatch/outwatch"
}

Outwatch

The Functional and Reactive Web-Frontend Library for Scala.js

import outwatch._
import outwatch.dsl._
import colibri._
import cats.effect.{IO, IOApp}

object Main extends IOApp.Simple {
  override def run = {
    val counter = Subject.behavior(0)
    val myComponent = div(
      button("+", onClick(counter.map(_ + 1)) --> counter),
      counter,
    )

    Outwatch.renderReplace[IO]!("#app", myComponent)
  }
}

In Outwatch, you can describe your whole web application without doing any side effect - you only run your application when rendering it.

• Write UI-components using pure functions
• Manage state in a referentially transparent way using cats-effect
• Built-in lightweight Observable and Subject types from colibri
• Seamlessly works with existing reactive programming libraries: ZIO, fs2, Airstream, scala.rx
• Low-boilerplate, many convenient helper functions
• Built on top of snabbdom, a virtual dom library

You will find interactive examples and explanations in our documentation.

Documentation

Bugs and Feedback

For bugs, questions and discussions please use GitHub Issues.

Community

We adopted the Scala Code of Conduct. People are expected to follow it when discussing Outwatch on the Github page, Gitter channel, or other venues.

LICENSE

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.