jwstegemann / Fritz2

fritz2 is an extremely lightweight, well-performing, independent library to build reactive web apps in Kotlin heavily depending on coroutines and flows.

fritz2 includes an intuitive way to build and render html-elements and styles using a type-safe dsl. You can easily create lightweight reactive html-components that are bound to an underlying model and automatically change whenever the model data changes:

val model = storeOf("init value")

render {
    div("some-css-class") {
        input {
            value(model.data)
            changes.values() handledBy model.update 
        }
        p {
            +"model value = "
            model.data.asText()
        }
    }
}

fritz2 implements precise data binding. This means that when parts of your data model change, exactly those and only those DOM-nodes depending on the changed parts will automatically change as well. No intermediate layer (like a virtual DOM) is needed. fritz2 requires no additional methods to decide which parts of your component have to be re-rendered:

Utilizing Kotlin's multiplatform-abilities, you'll write the code of your data classes only once and use it on your client and server (i.e. in a SpringBoot- or Ktor-Backend). This is also true for your model-validation-code, which can quickly become far more complex than your data model.

Key Features

• easy reactive one- and two-way-databinding (even for lists and deep nested structures)
• hassle-free redux-like state-handling
• model-validation and message handling
• integrated styling-dsl
• component-library
• routing (for SPAs, hash-based)
• backend-repositories (Rest APIs, WebSockets, LocalStorage, etc.)
• history / undo
• processing state ("spinning wheel")
• easy to learn
• documentation
• examples i.e. implementing the specification of TodoMVC

How to try it?

• Take a look at our hosted examples
• Or set up a new project on your own, following our documentation

Overall Goals

• staying lightweight (a few hundred lines of code for the core)
• keeping dependencies as low as possible (zero up to now!)
• generating elements, attributes, events for html from specification (w3c, mozilla, ...)
• make it as easy as possible to write reactive pwas in pure kotlin

Inspiration

fritz2 is hugely inspired by the great Binding.scala. Later we discovered that a lot of those concepts are described independently in Meiosis.

Leave us a star...

If you like the idea of a lightweight pure Kotlin implementation for building reactive web apps, please give us a star on github. Thank you.