ivy-create-external-widget

name	ivy-create-external-widget
description	Create a new Ivy External Widget backed by React npm packages. Use when the user asks to create a widget, external widget, React widget, custom component, or wrap an npm package as an Ivy widget. Scaffolds a C# + React project, installs npm dependencies, implements the widget class and React component, and verifies the build.
allowed-tools	Bash(dotnet:*) Bash(npm:*) Bash(npx:*) Bash(ivy:*) Read Write Edit Glob Grep
effort	high

ivy-create-external-widget

Create a new Ivy External Widget that wraps React npm packages with C# bindings.

Pre-flight: Read Learnings

If the file .ivy/learnings/ivy-create-external-widget.md exists in the project directory, read it first and apply any lessons learned from previous runs of this skill.

Reference Files

Read before implementing:

• references/AGENTS.md -- Ivy framework API reference (widgets, hooks, layouts, inputs, colors)

Reference Files

Before implementing, fetch the external widgets documentation using ivy docs with the query: "external widgets".

Workflow

1. Understand the widget purpose -- Ask the user what widget they need if it is not already clear from context.

2. Research npm packages -- Search the web for the best React npm package(s) for the use case. Packages MUST be open-source with a copyleft-compatible license (MIT, Apache-2.0, BSD, ISC, MPL-2.0, etc.). Look for packages that are well-maintained, popular, and have good TypeScript support.

3. Present options -- Show the user 2-4 npm package options. Include the package name, description, license, and weekly downloads if available. Ask the user to pick one.

4. Ask for a widget name -- Suggest a name similar to the chosen React package but without the word "React" in it. Names must be in PascalCase. Ask the user to confirm.

5. Determine the namespace -- If the working directory already has a .csproj file, extract the namespace from it. Otherwise, suggest Ivy.Widgets.<WidgetName> as a default namespace and ask the user to confirm.

6. Scaffold the widget project -- Create the widget project structure with:

   • [WidgetName].cs -- the C# widget class
   • frontend/ -- the React frontend project

   If the project already has a Widgets folder, move the new widget there and adjust the namespace accordingly.

7. Install npm dependencies -- Run in the frontend/ directory:

   cd [WorkingDirectory]/frontend && npm install [NpmPackages]
   

8. Implement the widget -- Follow the Ivy External Widget Guide below to create:

   • The C# widget class ([WidgetName].cs) -- define props, events, and extension methods that map to the npm package's API
   • The React component (frontend/src/[WidgetName].tsx) -- wrap the npm package component with Ivy's event system, using the conditional event firing pattern
   • The export file (frontend/src/index.ts) -- export the new component
   • A sample app (.samples/Apps/[WidgetName]App.cs)
   • Update README.md to document the widget, its props, events, and which npm packages it uses

9. Verify the build -- Run dotnet build to make sure the project compiles. Fix any errors.

---

Ivy External Widget Guide

Architecture

• C# Widget Class: Defines props, events, and the widget's API surface
• React Component: The frontend implementation loaded at runtime
• IIFE Bundle: The React component is bundled as an IIFE and exposed on window.{GlobalName}

C# Widget Definition

Create a .cs file with a record that inherits from WidgetBase<T>:

using Ivy;
using Ivy.Core;
using Ivy.Core.ExternalWidgets;

namespace MyNamespace;

[ExternalWidget("frontend/dist/{GlobalName}.js", ExportName = "MyWidget")]
public record MyWidget : WidgetBase<MyWidget>
{
    internal MyWidget()
    {
        Width = Size.Full();
        Height = Size.Full();
    }

    [Prop] public string? Title { get; set; }
    [Prop] public int Count { get; set; }
    [Prop] public bool Disabled { get; set; }

    [Event] public Func<Event<MyWidget>, ValueTask>? OnClick { get; set; }
    [Event] public Func<Event<MyWidget, string>, ValueTask>? OnChange { get; set; }
}

public static class MyWidgetExtensions
{
    public static MyWidget Title(this MyWidget widget, string title) =>
        widget with { Title = title };

    public static MyWidget Count(this MyWidget widget, int count) =>
        widget with { Count = count };

    public static MyWidget HandleClick(this MyWidget widget, Action handler) =>
        widget with { OnClick = _ => { handler(); return ValueTask.CompletedTask; } };

    public static MyWidget HandleChange(this MyWidget widget, Action<string> handler) =>
        widget with { OnChange = e => { handler(e.Value); return ValueTask.CompletedTask; } };
}

React Component

Create a .tsx file in frontend/src/:

import React from 'react';
import { IvyEventHandler } from './types';
import { getWidth, getHeight } from './styles';

interface MyWidgetProps {
  id: string;
  width?: string;
  height?: string;
  events?: string[];
  onIvyEvent: IvyEventHandler;
  title?: string;
  count?: number;
  disabled?: boolean;
}

export const MyWidget: React.FC<MyWidgetProps> = ({
  id,
  width = 'Full',
  height = 'Full',
  events = [],
  onIvyEvent,
  title,
  count,
  disabled,
}) => {
  const handleClick = () => {
    if (events.includes('OnClick')) {
      onIvyEvent('OnClick', id, []);
    }
  };

  const handleChange = (value: string) => {
    if (events.includes('OnChange')) {
      onIvyEvent('OnChange', id, [value]);
    }
  };

  const style: React.CSSProperties = {
    ...getWidth(width),
    ...getHeight(height),
  };

  return (
    <div style={style}>
      <h3>{title}</h3>
      <p>Count: {count}</p>
      <button onClick={handleClick} disabled={disabled}>Click me</button>
      <input onChange={(e) => handleChange(e.target.value)} />
    </div>
  );
};

Export the Component

Add the export to frontend/src/index.ts:

import { MyWidget } from './MyWidget';

if (typeof window !== 'undefined') {
  (window as Record<string, unknown>).{GlobalName} = {
    MyWidget,
  };
}

export { MyWidget };

Sample App

The .samples/ folder contains a runnable Ivy project. Create or update the app in .samples/Apps/[WidgetName]App.cs:

using Ivy;
using [Namespace];

namespace [Namespace].Samples.Apps;

[App]
public class MyWidgetApp : ViewBase
{
    public override object Build() =>
        new MyWidget();
}

Key Concepts

ExternalWidget Attribute

[ExternalWidget("frontend/dist/{GlobalName}.js", ExportName = "MyWidget")]

• First parameter: Path to the bundled JS file (embedded resource)
• ExportName: The name of the React component in the bundle's exports

Props vs Events

• [Prop]: Data passed from C# to React. PascalCase in C#, auto-converted to camelCase in React.
• [Event]: Callbacks from React to C#. Name with On prefix (e.g., OnClick, OnChange).

Event Handler Signature

In React, call onIvyEvent(eventName, widgetId, args):

• eventName: PascalCase with 'On' prefix (e.g., 'OnClick', 'OnChange')
• widgetId: Always pass id
• args: Array of arguments to pass to the C# handler

Conditional Event Firing

Always check the events array before firing:

const handleClick = () => {
  if (events.includes('OnClick')) {
    onIvyEvent('OnClick', id, []);
  }
};

Event Types

• Event<TWidget> -- event with no value. Properties: .Id (the widget ID)
• Event<TWidget, TValue> -- event with a value. Properties: .Id (the widget ID), .Value (the value of type TValue passed from React)

Use Event<TWidget> for simple notifications (e.g., button clicks) and Event<TWidget, TValue> when React needs to pass data back to C# (e.g., input changes, selections).

Key Namespaces

• Ivy -- WidgetBase<T>, ViewBase, Layout, Text, Icons, Size, Colors, ChromeSettings
• Ivy.Core -- PropAttribute, EventAttribute, Event<TWidget>, Event<TWidget, TValue>
• Ivy.Core.ExternalWidgets -- ExternalWidgetAttribute

Size Props

Use helper functions for sizing:

import { getWidth, getHeight } from './styles';

const style: React.CSSProperties = {
  ...getWidth(width),
  ...getHeight(height),
};

Smooth Input Handling Pattern

For input widgets, use local state with server sync to prevent laggy typing:

const [localValue, setLocalValue] = useState(value || '');
const [isFocused, setIsFocused] = useState(false);
const localValueRef = useRef(localValue);

useEffect(() => {
  if (!isFocused && value !== localValueRef.current) {
    queueMicrotask(() => setLocalValue(value || ''));
  }
}, [value, isFocused]);

useEffect(() => {
  localValueRef.current = localValue;
}, [localValue]);

const handleChange = useCallback((newValue: string) => {
  setLocalValue(newValue);
  if (events.includes('OnChange') && onIvyEvent) {
    onIvyEvent('OnChange', id, [newValue]);
  }
}, [events, onIvyEvent, id]);

Important Guidelines

• Never use <summary> XML documentation blocks
• Update README.md when making changes
• Create app files for each widget in .samples/Apps/[WidgetName]App.cs
• Use react-icons/lucide for icons
• Prefer shadcn building blocks when UI components are needed
• Default to full width and height (Width = Size.Full(), Height = Size.Full())
• Always include a default constructor (use internal)
• Default prop values must be specified both in C# and React

Post-run: Evaluate and Improve

After completing the task:

1. Evaluate: Did the build succeed? Were there compilation errors, unexpected behavior, or manual corrections needed during this run?
2. Update learnings: If anything required correction or was surprising, append a concise entry to .ivy/learnings/ivy-create-external-widget.md (create the file and .ivy/learnings/ directory if they don't exist). Each entry should note: the date, what went wrong, why, and what to do differently next time.
3. Skip if clean: If everything succeeded without issues, do not update the learnings file.