sapper/src/core/create_compilers.ts

import * as path from 'path';
import relative from 'require-relative';

export default function create_compilers({ webpack }: { webpack: string }) {
	const wp = relative('webpack', process.cwd());

	const serviceworker_config = try_require(path.resolve(`${webpack}/service-worker.config.js`));

	return {
		client: wp(
			require(path.resolve(`${webpack}/client.config.js`))
		),

		server: wp(
			require(path.resolve(`${webpack}/server.config.js`))
		),

		serviceworker: serviceworker_config && wp(serviceworker_config)
	};
}

function try_require(specifier: string) {
	try {
		return require(specifier);
	} catch (err) {
		if (err.code === 'MODULE_NOT_FOUND') return null;
		throw err;
	}
}