SWC Technology Intelligence

What is SWC?

SWC (Speedy Web Compiler) is an extensible Rust-based platform for fast compilation and bundling of JavaScript and TypeScript. It serves as a drop-in replacement for Babel and TypeScript compiler, offering 20x to 70x faster compilation speeds.

Created by Donny (kdy1) in 2019, SWC aims to be the compilation foundation for the next generation of JavaScript tooling. It's used by Next.js, Parcel, and Deno for their compilation needs. SWC focuses on being a compiler first, with bundling capabilities added through swcpack, making it highly specialized for transformation tasks.

Key Features

Compilation

• JavaScript: ES5/ES6+ transformation
• TypeScript: Type stripping and compilation
• JSX: React and other JSX transforms
• Decorators: Legacy and Stage 3 support

Performance

• Rust-Based: Native performance
• Parallel: Multi-threaded compilation
• Incremental: Efficient rebuilds
• Memory: Efficient memory usage

Transformations

• Minification: Built-in minifier
• Dead Code: Tree shaking support
• Polyfills: Automatic polyfill injection
• Module: ESM/CommonJS/AMD/UMD

Plugin System

• WASM-based plugins
• Rust plugin API
• Transform visitors
• Custom syntax extensions

Use Cases

Next.js Compilation

Next.js uses SWC as its default compiler. The Rust-based compiler dramatically speeds up both development and production builds compared to the previous Babel-based compilation.

Babel Replacement

Projects migrate from Babel to SWC for faster builds. Most Babel presets and plugins have SWC equivalents, making migration straightforward for standard configurations.

Jest Transformation

Test suites use @swc/jest for fast test compilation. Large test suites that took minutes with ts-jest compile in seconds, significantly reducing CI feedback time.

TypeScript Projects

Teams use SWC for type stripping alongside tsc --noEmit for type checking. This pattern provides both speed and type safety without compromising either.

Webpack Integration

Webpack builds use swc-loader instead of babel-loader. The drop-in replacement accelerates compilation while maintaining compatibility with webpack's ecosystem.

Build Tool Foundation

Tools like Parcel 2 and Deno use SWC internally. The compiler's reliability and speed make it a foundation for next-generation JavaScript tooling.

Code Examples

.swcrc Configuration

{
    "$schema": "https://json.schemastore.org/swcrc",
    "jsc": {
        "parser": {
            "syntax": "typescript",
            "tsx": true,
            "decorators": true,
            "dynamicImport": true
        },
        "transform": {
            "react": {
                "runtime": "automatic",
                "importSource": "react"
            },
            "decoratorMetadata": true,
            "legacyDecorator": true
        },
        "target": "es2020",
        "loose": false,
        "minify": {
            "compress": true,
            "mangle": true
        }
    },
    "module": {
        "type": "es6"
    },
    "sourceMaps": true
}

JavaScript API

const swc = require("@swc/core");

// Transform a file
const output = await swc.transformFile("./src/index.tsx", {
    jsc: {
        parser: { syntax: "typescript", tsx: true },
        transform: {
            react: { runtime: "automatic" }
        },
        target: "es2020"
    },
    sourceMaps: true
});

console.log(output.code);
console.log(output.map);

// Transform string
const result = await swc.transform(`
    const x: number = 1;
    const fn = (a: string) => a.toUpperCase();
`, {
    jsc: { parser: { syntax: "typescript" } }
});

webpack Configuration

// webpack.config.js
module.exports = {
    module: {
        rules: [
            {
                test: /\.(ts|tsx|js|jsx)$/,
                exclude: /node_modules/,
                use: {
                    loader: "swc-loader",
                    options: {
                        jsc: {
                            parser: {
                                syntax: "typescript",
                                tsx: true
                            },
                            transform: {
                                react: { runtime: "automatic" }
                            }
                        }
                    }
                }
            }
        ]
    }
};

Jest Configuration

// jest.config.js
module.exports = {
    transform: {
        "^.+\\.(t|j)sx?$": ["@swc/jest", {
            jsc: {
                parser: { syntax: "typescript", tsx: true },
                transform: { react: { runtime: "automatic" } }
            }
        }]
    }
};

Comparison and Ecosystem

SWC vs Babel

• Speed: SWC 20-70x faster
• Plugins: Babel more extensive ecosystem
• Compatibility: Babel broader browser support
• Config: Both similar configuration patterns

SWC vs esbuild

• Focus: SWC compilation, esbuild bundling
• Plugins: SWC more extensible
• Decorators: SWC better support
• Speed: Both extremely fast

Ecosystem

• @swc/core: Core compiler package
• @swc/jest: Jest transformer
• swc-loader: Webpack loader
• @swc/cli: Command line interface

Strengths

• Extremely fast compilation
• Babel-compatible configuration
• Full decorator support
• Growing ecosystem

Considerations

• No type checking (by design)
• Fewer plugins than Babel
• Plugin development requires Rust
• Some edge case differences from Babel