Customizing SWC

Jetpack uses SWC via swc-loader by default, because:

this way you get JSX support out of the box
you can be sure that the code you write will run in all the browsers you support

Jetpack uses the following SWC options:

{
  env: {
    targets: browsers.query(options),
    coreJs: 3,
    mode: 'entry',
    exclude: ['transform-typeof-symbol']
  },
  jsc: {
    parser: {
      jsx: true,
      exportDefaultFrom: true
    },
    transform: {},
  }
}

See lib/webpack.js.js for the exact configuration.

These options can be modified via jetpack.config.js:

module.exports = {
  webpack: (config, options) => {
    for (const rule of config.module.rules[0].oneOf) {
      if (rule.use) {
          for (const loader of rule.use) {
          if (loader.loader.includes('/swc-loader')) {
            loader.options.env.mode = 'usage'
          }
        }
      }
    }
  }
}