rollup/src/finalisers/umd.js

import { blank } from '../utils/object.js';
import { getName, quoteId, req } from '../utils/map-helpers.js';
import getInteropBlock from './shared/getInteropBlock.js';
import getExportBlock from './shared/getExportBlock.js';

export default function umd ( bundle, magicString, { exportMode, indentString }, options ) {
	if ( exportMode !== 'none' && !options.moduleName ) {
		throw new Error( 'You must supply options.moduleName for UMD bundles' );
	}

	const globalNames = options.globals || blank();

	let amdDeps = bundle.externalModules.map( quoteId );
	let cjsDeps = bundle.externalModules.map( req );
	let globalDeps = bundle.externalModules.map( module => {
		return 'global.' + (globalNames[ module.id ] || module.name);
	});

	let args = bundle.externalModules.map( getName );

	if ( exportMode === 'named' ) {
		amdDeps.unshift( `'exports'` );
		cjsDeps.unshift( `exports` );
		globalDeps.unshift( `(global.${options.moduleName} = {})` );

		args.unshift( 'exports' );
	}

	const amdParams =
		( options.moduleId ? `'${options.moduleId}', ` : `` ) +
		( amdDeps.length ? `[${amdDeps.join( ', ' )}], ` : `` );

	const cjsExport = exportMode === 'default' ? `module.exports = ` : ``;
	const defaultExport = exportMode === 'default' ? `global.${options.moduleName} = ` : '';

	const useStrict = options.useStrict !== false ? ` 'use strict';` : ``;

	const intro =
		`(function (global, factory) {
			typeof exports === 'object' && typeof module !== 'undefined' ? ${cjsExport}factory(${cjsDeps.join( ', ' )}) :
			typeof define === 'function' && define.amd ? define(${amdParams}factory) :
			${defaultExport}factory(${globalDeps});
		}(this, function (${args}) {${useStrict}

		`.replace( /^\t\t/gm, '' ).replace( /^\t/gm, magicString.getIndentString() );

	// var foo__default = 'default' in foo ? foo['default'] : foo;
	const interopBlock = getInteropBlock( bundle );
	if ( interopBlock ) magicString.prepend( interopBlock + '\n\n' );

	const exportBlock = getExportBlock( bundle.entryModule, exportMode );
	if ( exportBlock ) magicString.append( '\n\n' + exportBlock );

	return magicString
		.trim()
		.indent( indentString )
		.append( '\n\n}));' )
		.prepend( intro );
}