Add --downlevel option to manually enable IE9+ compat

Author: developit

src/cli.js

@@ -17,7 +17,8 @@ prog
 	.version(version)
 	.option('--files', 'Minimatch pattern for test files')
 	.option('--headless', 'Run using Chrome Headless', true)
-	.option('--coverage', 'Report code coverage of tests', true);
+	.option('--coverage', 'Report code coverage of tests', true)
+	.option('--downlevel', 'Downlevel syntax to ES5');
 
 prog
 	.command('run [...files]', '', { default: true })

src/configure.js

@@ -17,6 +17,7 @@ const WEBPACK_MAJOR = parseInt(WEBPACK_VERSION.split('.')[0], 10);
  * @param {Boolean} [options.watch=false] - Start a continuous test server and retest when files change
  * @param {Boolean} [options.coverage=false] - Instrument and collect code coverage statistics
  * @param {Object} [options.webpackConfig] - Custom webpack configuration
+ * @param {Boolean} [options.downlevel=false] - Downlevel/transpile syntax to ES5
  */
 export default function configure(options) {
 	let cwd = process.cwd(),
@@ -235,6 +236,7 @@ export default function configure(options) {
 
 		webpack: {
 			devtool: 'cheap-module-eval-source-map',
+			// devtool: 'module-source-map',
 			mode: webpackConfig.mode || 'development',
 			module: {
 				// @TODO check webpack version and use loaders VS rules as the key here appropriately:

src/lib/babel-loader.js

@@ -10,7 +10,7 @@ export default function babelLoader(options) {
 						browsers: [
 							'last 2 Chrome versions',
 							'last 2 Firefox versions',
-							options.browsers && String(options.browsers).match(/(\bie(\b|\d)|internet.explorer)/gi) && 'ie>=9'
+							(options.downlevel || options.browsers && String(options.browsers).match(/(\bie(\b|\d)|internet.explorer)/gi)) && 'ie>=9'
 						].filter(Boolean)
 					},
 					corejs: 2,