Syntax Downgrade and Polyfill

By default, Farm will downgrade to ES2017(native support async/await) and inject necessary polyfills automatically in production mode.

note

By default, Farm won't do transformation and inject polyfills for modules under node_modules/, if you need to downgrade syntax and inject polyfills for node_modules/ you can use compilation.presetEnv.include.

Configuring targetEnv

Farm provide a normalized output.targetEnv option to configure the target execution environment of your application. Farm will perform properly syntax downgrade and polyfill injection for your target environment automatically. For example:

farm.config.ts

export default {
  compilation: {
    output: {
      targetEnv: 'browser-legacy'
    }
  },
};

Farm will compile your application to legacy browsers(ES5):

• Compile all Js/Jsx/Ts/Tsx modules to ES5, and inject all polyfills(Promise, regenerator-runtime and so on).
• Add prefix for all css/scss/less modules, for example, --webkit-.

Farm supports many normalized targetEnv options like browser-modern, browser-es2017, browser-es2015, node16, node-legacy, etc. By default, targetEnv is browser-es2017. Refer to output.targetEnv.

note

You may need to install core-js@3 or regeneration-runtime manually if polyfill is needed. Try run pnpm add core-js if you met something error like can not resolve 'core-js/modules/xxx'

Configuring Syntax and Polyfill Separately

Internally, targetEnv just presets of presetEnv, script.target and css.prefixer. You can configure them more precisely if you need.

Configuring presetEnv

You can use compilation.presetEnv to custom syntax downgrade and polyfill injection. By default all modules under node_modules will be ignored. Using include to add extra modules that need to be polyfilled.

farm.config.ts

export default {
   compilation: {
     presetEnv: {
      // include a package under node_modules
      include: ['node_modules/package-name'],
      options: {
        targets: "Chrome >= 48"
      }
     }
   },
};

Note that if your project does not require browser compatibility, you can use set a looser value for targets, then less polyfills will be injected and output sizes will be smaller.

Refer to compilation.presetEnv for more options.

Configuring script.target

script.target is used to control the target env when generate code. If you want to downgrade your project to ES5, you should set both:

farm.config.ts

export default {
   compilation: {
     script: {
      target: 'ES5'
     },
     presetEnv: {
      // include a package under node_modules
      include: ['node_modules/package-name'],
      options: {
        targets: "> 0.25%, not dead"
      }
     }
   },
};