# WebAssembly Feature Detection

A small library to detect which features of WebAssembly are supported.

- ✅ Runs in browsers, Node and Deno
- ✅ Tree-shakable (only bundle the detectors you use)
- ✅ Provided as an ES6, CommonJS and UMD module.
- ✅ CSP compatible
- ✅ All detectors add up to only ~<%= gzippedSize %>B gzipped

## Installation

```
npm install -g wasm-feature-detect
```

## Usage

```html
<script type="module">
  import { simd } from "wasm-feature-detect";

  if (await simd()) {
    /* SIMD support */
  } else {
    /* No SIMD support */
  }
</script>
```

### Hotlinking from Unpkg

```html
<script type="module">
  import { simd } from "https://unpkg.com/wasm-feature-detect?module";
  // ...
</script>
```

If required, there’s also a UMD version

```html
<script src="https://unpkg.com/wasm-feature-detect/dist/umd/index.js"></script>
<script>
  if (await wasmFeatureDetect.simd()) {
    // ...
  }
</script>
```

## Detectors

All detectors return a `Promise<bool>`.

| Function | Proposal |
| --- | --- |
<% for (let detector of detectors) { _%>
| `<%= detector.func %>()` | [<%= detector.name %>](<%= detector.proposal %>) |
<%_ } %>

## Why are all the tests async?

The _technical_ reason is that some tests might have to be augmented to be asynchronous in the future. For example, Firefox is planning to [make a change][ff coop] that would require a `postMessage` call to detect SABs, which are required for threads.

The _other_ reason is that you _should_ be using `WebAssembly.compile`, `WebAssembly.instantiate`, or their streaming versions `WebAssembly.compileStreaming` and `WebAssembly.instantiateStreaming`, which are all asynchronous. You should already be prepared for asynchronous code when using WebAssembly!

## Contributing

If you want to contribute a new feature test, all you need to do is create a new folder in `src/detectors` and it will be automatically picked up. The folder may contain a `module.wat` file, which will be compiled using [`wabt.js`](https://github.com/AssemblyScript/wabt.js).

```wat
;; Name: <Name of the feature for the README>
;; Proposal: <Link to the proposal’s explainer/repo>
;; Features: <Space-separated list of WasmFeatures from wabt.js>

(module
  ;; More WAT code here
)
```

The folder can also contain an optional `index.js` file, whose default export must be an async function. This function can do additional testing in JavaScript and must return a boolean. See the “threads” detector as an example.
It must contain at least one of `module.wat` or `index.js`.

[ff coop]: https://groups.google.com/forum/#!msg/mozilla.dev.platform/IHkBZlHETpA/dwsMNchWEQAJ
[wat2wasm]: https://github.com/webassembly/wabt

---

License Apache-2.0