Rescript vanilla web components (classes)

Is there a way to model using pure rescript? guess no, as there is no class construct equivalent
@@jsxConfig({ version: 4, mode: “automatic” })

Correct. There’s not a way to create classes in pure rescript.

Is there a way to bind rescript to js class definitions?

Sure. In the React component case, it’s pretty easy. Here’s an implementation of an ErrorBoundary that should work in the playground:

module ErrorBoundary = {
  %%raw(`
class ErrorBoundaryImpl extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError(error) {
    // Update state so the next render will show the fallback UI.
    return { hasError: true };
  }

  componentDidCatch(error, info) {
    // Example "componentStack":
    //   in ComponentThatThrows (created by App)
    //   in ErrorBoundary (created by App)
    //   in div (created by App)
    //   in App
    console.log(error, info.componentStack);
  }

  render() {
    if (this.state.hasError) {
      // You can render any custom fallback UI
      return this.props.fallback;
    }

    return this.props.children;
  }
}
  `)
  @react.component
  external make: (
    ~fallback: React.element,
    ~children: React.element
  ) => React.element = "ErrorBoundaryImpl"
}

let badCall: () => 'a = %raw(`
  () => { throw "Oh boy." }
`)

module ChildComponent = {
  @react.component
  let make = (~shouldError) => {
    if shouldError {
      badCall()
    }
    <div style={{color: "green"}}>
      {React.string("All good here!")}
    </div>
  }
}

module App = {
  @react.component
  let make = () => 
    <div>
      <ErrorBoundary fallback={<div style={{color: "red"}}>{React.string("Never needed!")}</div>}>
        <ChildComponent shouldError={false} />
      </ErrorBoundary>
      <ErrorBoundary fallback={<div style={{color: "red"}}>{React.string("An error was thrown here!")}</div>}>
        <ChildComponent shouldError={true} />
      </ErrorBoundary>
    </div>
}