Assistant UI Svelte Project 2025

Project Overview

What I Built

I built a Svelte 5 + SvelteKit 2 scaffold for a ChatGPT-style chat interface: sticky, pill-shaped composer; a scrollable message thread with clear user/assistant alignment; smooth auto-scroll to the latest message; and accessible, keyboard-friendly interaction. The experience mirrors ChatGPT’s proven UX so it feels familiar and intuitive.

Beyond the surface UI, it is intentionally designed as a standalone, reusable foundation that can plug into any conversational AI or agent backend. The layout and component architecture are structured for streaming APIs, richer message rendering, and multi-turn state. It draws heavy inspiration from assistant-ui and is tailored for reuse in my other work, notably DOC_Project_2025.

Why I Built It

• Skill goal: Learn Svelte while creating a production-ready chat UI scaffold.
• Practical goal: Build a reusable, well-structured component library for future LLM-powered tools.

Technical Overview

System Architecture

The UI follows a modular, state-driven design built around Svelte 5 runes:

• Scrollable message list and sticky-bottom composer
• Auto-scroll on new messages
• Accessible, keyboard-friendly input
• Visual consistency between empty and active states

Key Components

Message Thread: A scrollable message list with clear user/assistant alignment and smooth auto-scroll behavior.

Composer: A sticky, pill-shaped input component designed for keyboard-first interaction and visual consistency.

State & Effects: Uses Svelte runes ($effect) to update scroll position when messages change.

Code in Action: Message Flow Example

1. Initial UI State

• Empty message thread
• Composer visible and focused
• Keyboard-ready interaction

2. User Sends a Message

• Prevents empty sends
• Appends message to state
• Auto-scrolls to latest message

3. Assistant Response (Mocked)

• Response is added to the thread
• UI auto-scrolls again
• Layout remains stable

How the UI Works

1. Message State

messages = [...messages, newMessage];

2. Auto-Scroll

$effect(() => {
  scrollTop = scrollHeight;
});

3. Input Handling

• Disabled state when input is empty
• Keyboard-friendly submit behavior

Project Structure & File Guide

Directory Overview

assistant_ui_svelte/
│
├── src/
│   ├── lib/
│   │   ├── components/
│   │   │   ├── ChatShell.svelte
│   │   │   ├── MessageList.svelte
│   │   │   └── Composer.svelte
│   │   └── styles/
│   ├── routes/
│   │   └── +page.svelte
│   └── app.css
│
├── static/
├── package.json
├── svelte.config.js
├── vite.config.ts
└── README.md

Current Status

The ChatGPT-style framework is complete and running locally, with:

• Scrollable message list and sticky-bottom composer
• Auto-scroll on new messages
• Accessible, keyboard-friendly input
• Visual consistency between empty and active states

Responses are currently mocked—the architecture is ready for a streaming LLM backend.

Challenges and How I Solved Them

• Keeping the composer fixed while allowing scrollable content: Solved with a two-row CSS Grid and position: sticky shell.
• Reliable auto-scroll to latest message: Used Svelte runes ($effect) to update scroll position on message change.
• Preventing empty sends & ensuring keyboard focus: Added conditional disabled state and explicit focus handling.
• Maintaining visual consistency between empty and chat views: Reused composer styles across both UI states.
• ARM64 Windows dependency warnings: Implemented a clean reinstall flow (clear cache, remove lockfile and node_modules, reinstall).

Future Possibilities

• Real LLM/agent backend with streaming
• Theme system (dark mode, high-contrast mode)
• Persistent conversations (LocalStorage, IndexedDB, or server DB)
• Rich message rendering (Markdown, syntax highlighting, file attachments)
• Advanced keyboard UX (shortcuts, multi-line editing, resend)
• Testing suite (Vitest, Playwright) + CI/CD pipeline

TL;DR

A reusable Svelte 5 + SvelteKit 2 ChatGPT-style chat UI (sticky composer, scrollable aligned thread, auto-scroll, a11y) designed to plug into real LLM/agent backends; currently mocked but architected for streaming, richer messages, and multi-turn state—ready to reuse across projects like DOC_Project_2026.

Project Duration: August 2025
Technologies: Svelte 5, SvelteKit 2, Vite 7, TypeScript, Less, Node.js, npm, Git