swc-plugin-transform-async-to-ng-generator

SWC plugin to transform async functions to generator functions wrapped with _ngAsyncToGenerator for AngularJS $q compatibility.

Why?

AngularJS uses $q for promises, which integrates with the digest cycle. Native async/await returns native Promises that don't trigger Angular's digest cycle. This plugin transforms async functions to use a custom wrapper that uses $q when available.

Installation

npm install swc-plugin-transform-async-to-ng-generator @swc/core

Usage

In your SWC config:

{
  jsc: {
    experimental: {
      plugins: [
        ["swc-plugin-transform-async-to-ng-generator", {}]
      ]
    }
  }
}

Runtime Requirement

You need to include the _ngAsyncToGenerator runtime helper in your application. See ngAsyncToGenerator.js for the implementation.

Transformation Examples

Async Function Declaration

// Input
async function fetchData() {
    const result = await fetch('/api');
    return result;
}

// Output
function fetchData() {
    return _fetchData.apply(this, arguments);
}
function _fetchData() {
    _fetchData = _ngAsyncToGenerator(function* () {
        const result = yield fetch('/api');
        return result;
    });
    return _fetchData.apply(this, arguments);
}

Async Arrow Function

// Input
const fetchData = async () => {
    const result = await fetch('/api');
    return result;
};

// Output
const fetchData = (function () {
    var _ref = _ngAsyncToGenerator(function* () {
        const result = yield fetch('/api');
        return result;
    });
    return function () {
        return _ref.apply(this, arguments);
    };
})();

Async Class Method

// Input
class Service {
    async load() {
        const data = await this.fetch();
        return data;
    }
}

// Output
class Service {
    load() {
        var _this = this;
        return _ngAsyncToGenerator(function* () {
            const data = yield _this.fetch();
            return data;
        })();
    }
}

Building

# Install Rust (stable) and wasm32-wasip1 target
rustup target add wasm32-wasip1

# Build
npm run build

The output wasm file will be at target/wasm32-wasip1/release/swc_plugin_transform_async_to_ng_generator.wasm.

Upgrading Dependencies

When upgrading Rust dependencies (e.g., updating swc_core version in Cargo.toml), you need to temporarily disable offline mode:

CARGO_NET_OFFLINE=false cargo build --target wasm32-wasip1 --release

This allows Cargo to fetch new crate versions from the registry.

Compatibility

This plugin is compatible with @swc/core version 1.15.x (swc_core v54.0.0).

License

MIT