The cleanest way to interact with WCLAPs in the browser is to write a C++ WASM host, which then exposes a simpler API to JS. This keeps all the CLAP-specific structures in the "native" world.

The cpp/ subdirectory provides wclap-js-instance(a .h/.cpp pair) for building the native side of your WCLAP host.

It provides an Instance implementation (as defined in wclap-cpp) which abstracts all the WCLAP interactions (e.g. calling WCLAP functions, reading/writing structures in its memory).

It also provides a JavaScript library (ES6 module: wclap-js/wclap.mjs) which can load any WASM hosts written using the above C++ library, and handles the corresponding WebAssembly instances.

All functions are asynchronous aside from host.getWorkerData() and the two .initObj() methods. The top-level exported functions are:

• getHost() / getWclap() - takes a URL and returns an "initialisation object" (including a compiled WebAssembly module) for the host or a WCLAP module
• startHost(initObj, ?hostImports, ?createWorker) - takes the initialisation object and (if supported) a function to create new Workers, and returns a Host.
• runThread(threadData, hostImports, createWorker) - to be called from any Workers that you start

This is the object returned from startHost(). It has the following properties/methods:

• .hostInstance - the actual WebAssembly.Instance. Any custom exports from your C++ will be in .hostInstance.exports.
• .hostMemory - hosts's memory, whether imported or exported
• .startWclap(wclapInit, ?createWorker) - takes an initialisation object and returns a Wclap
• .getWorkerData() - see createWorker() below
• .shared - whether this host (currently) supports threads
• .initObj() - an initialisation object which can be passed across Workers to create a matching Host. If cross-origin isolated, this will join the existing host as a new thread.

This is the object returned from host.startWclap(). It has the following properties/methods:

• .ptr - this corresponds to the Instance * in the host's C++ side
• .memory - the WCLAP instance's memory
• .shared - whether this WCLAP supports threads
• .initObj() - an initialisation object which can be passed across Workers to create a matching Wclap. If cross-origin isolated, this will join as a new thread.

This function (supplied either when starting the host, or the Wclap) is called when the Wclap wants to start a new thread. It must (synchronously) return a true-ish value if successful.

The threadData doesn't contain any shared memory or modules, which means it can be passed back from the AudioWorklet (which is otherwise quite restricted).

To get the data which should actually be passed to the new Worker, call host.getWorkerData(threadData). On the new Worker, this should be passed to runThread().