#lib.autoExtension

• Type: boolean
• Default: true

Whether to automatically set the file extension based on the format option in the JavaScript output files.

#Default extension

By default that when autoExtension is set to true, the file extension will be:

• .js with esm format and .cjs with cjs format when type: module in package.json.

• .js with cjs format and .mjs with esm format when type: commonjs or no type field in package.json.

When autoExtension is set to false, the file extension will be default to .js.

#Customize extension

You can set autoExtension to false and use output.filename to customize the JavaScript output files.

export default defineConfig({
  lib: [
    {
      format: 'cjs',
      autoExtension: false,
      output: {
        filename: {
          js: '[name].cjs',
        },
      },
    },
    {
      format: 'esm',
      output: {
        filename: {
          js: '[name].mjs',
        },
      },
    },
  ],
});