#lib.syntax

• Type:

type EcmaScriptVersion =
  | 'es5'
  | 'es6'
  | 'es2015'
  | 'es2016'
  | 'es2017'
  | 'es2018'
  | 'es2019'
  | 'es2020'
  | 'es2021'
  | 'es2022'
  | 'es2023'
  | 'es2024'
  | 'esnext';

type Syntax = EcmaScriptVersion | string[];

• Default: 'esnext'
• CLI: --syntax <value> (repeatable, e.g. --syntax es2018 or --syntax="node 14" --syntax="Chrome 103")

Configure the syntax to which JavaScript and CSS will be downgraded.

See Output Compatibility - Syntax Downgrade for more details.

#Set ECMAScript version

You can set the ECMAScript version directly, such as es2015, es2022, etc.

export default {
  lib: [
    {
      syntax: 'es2015',
    },
  ],
};

#Set browserslist query

You can also set the Browserslist query, such as last 2 versions, > 1%, node >= 16, chrome >= 80, etc.

export default {
  lib: [
    {
      syntax: ['last 2 versions', '> 1%'],
    },
  ],
};

#Mix ECMAScript version and browserslist query

You can also mix ECMAScript version and Browserslist query, such as es2015 and node 20. Rslib will turn ECMAScript Version into Browserslist query, and then merge them together.

export default {
  lib: [
    {
      syntax: ['es2015', 'node 20'],
    },
  ],
};