Announcing bindable.scala, a library to create user-friendly Binding.scala components



When creating a Binding.scala component that accepts parameters or “holes”, it is difficult to determine the types of those parameters.

For example, the following component accepts two Binding as parameters:

@dom def myComponent1(title: Binding[String], children: Binding[BindingSeq[Node]]) = {
  <div title={title.bind}>

By typing parameters as Bindings, myComponent1 allows partial rendering whenever the value of title or children is changed. Unfortunately, it is too verbose to use myComponent1 for simple use cases when the parameters are constants.

// Does not compile
@dom def myUseCases1 = myComponent1("My Title", <img/>).bind

// Compiles, but too verbose
@dom def myUseCases2 = myComponent1(Constant("My Title"), Constant(Constants(<img/>))).bind

In this library, we introduced two type classes, Bindable and BindableSeq, to allow heterogeneous types of parameters for a component.


Step 1: adding the following settings into your build.sbt

addCompilerPlugin("org.spire-math" %% "kind-projector" % "latest.release")

libraryDependencies += "com.thoughtworks.binding" %%% "bindable" % "latest.release"

Step 2: creating a component that accepts bindable parameters

import com.thoughtworks.binding.bindable._
import org.scalajs.dom.raw._
@dom def myComponent2[Title: Bindable.Lt[?, String], Children: BindableSeq.Lt[?, Node]](title: Title, children: Children) = {
  <div title={title.bind}>

Step 3: using the component with any parameters that can be converted to Binding or BindingSeq

import com.thoughtworks.binding._, Binding._
@dom def myUseCases3 = myComponent2("My Title", <img/>).bind
@dom def myUseCases4 = myComponent2(Constant("My Title"), Constant(Constants(<img/>))).bind
@dom def myUseCases5 = myComponent2("My Title", <img/><img/>).bind
@dom def myUseCases6 = myComponent2("My Title", Binding(<img/><img/>)).bind

Unlike use cases of myComponent1, all the above use cases of myComponent2 compile now, because of the Bindable and BindableSeq type classes.