Add env query parameter. (#368)

fix #283

Signed-off-by: Maël Lavault <mael.lavault@universalavenue.com>

README.md

@@ -1,6 +1,6 @@
-# babel-loader 
-[![NPM Status](https://img.shields.io/npm/v/babel-loader.svg?style=flat)](https://www.npmjs.com/package/babel-loader) 
-[![Build Status](https://travis-ci.org/babel/babel-loader.svg?branch=master)](https://travis-ci.org/babel/babel-loader) 
+# babel-loader
+[![NPM Status](https://img.shields.io/npm/v/babel-loader.svg?style=flat)](https://www.npmjs.com/package/babel-loader)
+[![Build Status](https://travis-ci.org/babel/babel-loader.svg?branch=master)](https://travis-ci.org/babel/babel-loader)
 [![Build Status](https://ci.appveyor.com/api/projects/status/vgtpr2i5bykgyuqo/branch/master?svg=true)](https://ci.appveyor.com/project/danez/babel-loader/branch/master)
 [![codecov](https://codecov.io/gh/babel/babel-loader/branch/master/graph/badge.svg)](https://codecov.io/gh/babel/babel-loader)
   > Babel is a compiler for writing next generation JavaScript.
@@ -89,6 +89,8 @@ module: {
 
   * `babelrc`: Default `true`.  When `false`, will ignore `.babelrc` files (except those referenced by the `extends` option).
 
+  * `forceEnv`: Default will resolve BABEL_ENV then NODE_ENV. Allow you to override BABEL_ENV/NODE_ENV at the loader level. Useful for isomorphic applications with different babel configuration for client and server.
+
   __Note:__ The `sourceMap` option is ignored, instead sourceMaps are automatically enabled when webpack is configured to use them (via the `devtool` config option).
 
 ## Troubleshooting

src/index.js

@@ -88,10 +88,12 @@ module.exports = function(source, inputSourceMap) {
       babelrc: exists(userOptions.babelrc) ?
           read(userOptions.babelrc) :
           resolveRc(path.dirname(filename)),
-      env: process.env.BABEL_ENV || process.env.NODE_ENV,
+      env: userOptions.forceEnv || process.env.BABEL_ENV || process.env.NODE_ENV,
     }),
   };
 
+  delete userOptions.forceEnv;
+
   const options = assign({}, defaultOptions, userOptions);
 
   if (userOptions.sourceMap === undefined) {