Qt for WebAssembly▲

WebAssembly is a binary format that allows sand-boxed executable code in web pages. This format is nearly as fast as native machine code, and is now supported by all major web browsers.

Qt for WebAssembly is a platform plugin that lets you build Qt applications, which can be integrated into your web pages. It doesn't require any client-side installations and reduces the server-side resource usage.

Getting Started with Qt for WebAssembly▲

 

Install Emscripten▲

emscripten is a toolchain for compiling to asm.js and Webassembly. It lets you run Qt on the web at near-native speed without plugins.

Refer to the emscripten documentation for the installation procedure.

After installation, you should have emscripten in your path. Check this with the following command:

 
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em++ --version

Build Qt from the sources▲

Download the Qt 5.12 sources and build Qt from source. Specify that we are cross-compiling for wasm using emscripten:

 
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$ ~/Qt/5.12.0/Src/configure -xplatform wasm-emscripten -nomake examples -prefix $PWD/qtbase
$ make module-qtbase module-qtdeclarative [other modules]

The Qt build is a static build, and does not support threads.

Build your application▲

 
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$ /path/to/qt-wasm/qtbase/bin/qmake
$ make

This generates the following files:

Generated file

Brief Description

app.html

HTML container

qtloader.js

JS API for loading Qt apps

app.js

JS API for loading Qt apps

app.wasm

emscripten app binary

When deploying the app, the compression is typically handled on the server side. We recommend to compress the wasm binaries because this typically reduces the size of the binary by 50 %.

Some examples▲

Limitations▲

The most important limitation is that the Qt build is static, and does not support threads.

For further info, refer to Known_issues_and_platform_notes.

External resources▲

Licenses