Learn QT-WEBASSEMBLY with Real Code Examples

Updated Nov 25, 2025

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Explain

Qt-WASM compiles Qt C++ applications into WebAssembly (WASM) bytecode for browser execution.

Supports Qt Widgets, Qt Quick (QML), and standard Qt modules for UI and logic.

Runs in any modern browser without additional plugins or extensions.

Enables access to browser APIs like WebSockets, IndexedDB, and localStorage through Qt abstractions.

Used for deploying desktop-grade GUI apps on the web with near-native performance.

Core Features

Qt application compiled to WebAssembly using Emscripten

Qt Quick/QML rendering in browser canvas

Qt event loop mapped to browser event system

File and network access via browser APIs

Integration with JavaScript for browser-specific interactions

Basic Concepts Overview

Qt Widgets – traditional desktop-style GUI components

Qt Quick/QML – declarative UI for modern apps

Emscripten – compiler toolchain for C++ -> WASM

WebAssembly – binary format for browser execution

Qt WebAssembly Kit – preconfigured build target for Qt

Project Structure

src/ - C++ or QML source files

qml/ - QML modules if using Qt Quick

build/ - compiled WASM artifacts

index.html - generated HTML loader

assets/ - images, audio, fonts, or other resources

Building Workflow

Write Qt C++ or QML application

Configure WebAssembly kit in Qt Creator

Compile project with Emscripten target

Deploy generated .html and .wasm files to web server

Run app in modern web browser

Difficulty Use Cases

Beginner: run basic Qt Widget app in browser

Intermediate: deploy Qt Quick interface with animations

Advanced: integrate WebSockets or IndexedDB

Expert: optimize large GUI app for WASM performance

Auditor: debug memory and performance in browser

Comparisons

Qt-WASM vs Emscripten C++ apps: Qt provides UI framework

Qt-WASM vs React/Angular: Qt allows C++ GUI in browser

Qt-WASM vs WebGL games: Qt offers full app framework, not just graphics

Qt-WASM vs Pyodide: C++ vs Python WASM execution

Qt-WASM vs Flutter Web: C++ Qt vs Dart/Flutter GUI in browser

Versioning Timeline

2018 – Initial experiments with Qt-WASM

2019 – Qt 5.13 preliminary WASM support

2020 – Qt 5.15 stabilized WASM support

2021 – Qt 6 WebAssembly target introduced

2022–2025 – Enhanced module support and performance optimizations

Glossary

WebAssembly (WASM) - binary format for browser execution

Emscripten - C++ -> WASM compiler toolchain

Qt Quick/QML - declarative UI module

Qt WebAssembly Kit - build target for Qt apps