Add DOMRefTypes example

[MaxDesiatov]

This provides an example of DOM manipulation using reference types. With all optimizations enabled, final .build/release/RefsTest.wasm binary built using Embedded Swift SDK is only 1.2 kB.

[MaxDesiatov]

@kateinoigakukun would you have a moment to review this at some point?

[zaneenders]

Hi, I'm wondering what you did to get 1.2kb? I'm seeing 23kb with the following command.

swift build -c release  --swift-sdk swift-6.2-DEVELOPMENT-SNAPSHOT-2025-09-06-a_wasm-embedded

Swift version 6.2-dev (LLVM 1b5a5a47cc92b04, Swift 7ec75e941fbfc24)
Target: aarch64-unknown-linux-gnu
Build config: +assertions

[MaxDesiatov]

@zaneenders you have to pass -c release to your swift build invocation, e.g. this way:

swift build --swift-sdk "$(swiftc -print-target-info | jq -r '.swiftCompilerTag')_wasm-embedded" \
  -c release

Then run wasm-opt with these options:

wasm-opt .build/release/*.wasm -Oz --strip-debug --inlining-optimizing -cw -c --dae-optimizing \
  --local-cse --gufa-optimizing -o opt.wasm

Verify the final size:

wc -c opt.wasm

Output for the last command for me is 1297 bytes when using swift-DEVELOPMENT-SNAPSHOT-2025-09-07-a and wasm-opt version 124.

[zaneenders]

That worked. Thank you!