rollup/src/finalisers/cjs.js

import { keys } from '../utils/object';

export default function cjs ( bundle, magicString, exportMode ) {
	let intro = `'use strict';\n\n`;

	// TODO handle empty imports, once they're supported
	const importBlock = bundle.externalModules
		.map( module => {
			let requireStatement = `var ${module.name} = require('${module.id}');`;

			if ( module.needsDefault ) {
				requireStatement += '\n' + ( module.needsNamed ? `var ${module.name}__default = ` : `${module.name} = ` ) +
					`'default' in ${module.name} ? ${module.name}['default'] : ${module.name};`;
			}

			return requireStatement;
		})
		.join( '\n' );

	if ( importBlock ) {
		intro += importBlock + '\n\n';
	}

	magicString.prepend( intro );

	let exportBlock;
	if ( exportMode === 'default' && bundle.entryModule.exports.default ) {
		exportBlock = `module.exports = ${bundle.entryModule.getCanonicalName('default')};`;
	} else if ( exportMode === 'named' ) {
		exportBlock = keys( bundle.entryModule.exports )
			.map( key => {
				const specifier = bundle.entryModule.exports[ key ];
				const name = bundle.entryModule.getCanonicalName( specifier.localName );

				return `exports.${key} = ${name};`;
			})
			.join( '\n' );
	}

	if ( exportBlock ) {
		magicString.append( '\n\n' + exportBlock );
	}

	return magicString;
}