override values from .env with values form environment variables

babel-plugin-dotenv/index.js

@@ -3,6 +3,8 @@ var fs = require('fs');
 var sysPath = require('path');
 var process = require('process');
 
+var environmentCopy = Object.assign({}, process.env)
+
 module.exports = function (data) {
     var t = data.types;
 
@@ -30,13 +32,19 @@ module.exports = function (data) {
                     }
                     var importedId = specifier.imported.name
                     var localId = specifier.local.name;
-                    if(!(config.hasOwnProperty(importedId))) {
-                      throw path.get('specifiers')[idx].buildCodeFrameError('Try to import dotenv variable "' + importedId + '" which is not defined in any ' + configFile + ' files.')
+                    if(!(config.hasOwnProperty(importedId)) && !environmentCopy.hasOwnProperty(importedId)) {
+                      throw path.get('specifiers')[idx].buildCodeFrameError(
+                        'Try to import dotenv variable "'
+                        + importedId
+                        + '" which is not defined in any '
+                        + configFile
+                        + ' files or as an environment variable.'
+                      )
                     }
 
                     var binding = path.scope.getBinding(localId);
                     binding.referencePaths.forEach(function(refPath){
-                      refPath.replaceWith(t.valueToNode(config[importedId]))
+                      refPath.replaceWith(t.valueToNode(environmentCopy[importedId] || config[importedId]))
                     });
                   })
 

babel-plugin-dotenv/test/fixtures/override-value/.babelrc

@@ -0,0 +1,10 @@
+{
+  "plugins": [
+    "babel-plugin-transform-es2015-modules-commonjs",
+    ["../../../", {
+      "replacedModuleName": "babel-dotenv",
+      "configDir": "test/fixtures/default"
+    }]
+  ]
+}
+

babel-plugin-dotenv/test/fixtures/override-value/.env

@@ -0,0 +1,2 @@
+FOO_ENV=abc123
+

babel-plugin-dotenv/test/fixtures/override-value/source.js

@@ -0,0 +1,2 @@
+import { FOO_ENV } from 'babel-dotenv';
+console.log(FOO_ENV);

babel-plugin-dotenv/test/test.js

@@ -11,11 +11,19 @@ var createPluginsWithConfigDir = function(configDir) {
 }
 
 describe('myself in some tests', function() {
-  it('should throw if variable not exist', function() {
+  before(function() {
+    process.env.FOO_ENV = 'foo'
+  })
+
+  after(function() {
+    delete process.env.FOO_ENV
+  })
+
+  it('should throw if variable not exist and no environemnt variable is defined', function() {
     expect(function(){
       babel.transformFileSync('test/fixtures/variable-not-exist/source.js')
     }).to.throwException(function (e) {
-      expect(e.message).to.contain("Try to import dotenv variable \"foo\" which is not defined in any .env files.");
+      expect(e.message).to.contain("Try to import dotenv variable \"foo\" which is not defined in any .env files or as an environment variable.");
     });
   });
 
@@ -27,6 +35,11 @@ describe('myself in some tests', function() {
     });
   });
 
+  it('should override values defined in .env with environment variable', function() {
+    var result = babel.transformFileSync('test/fixtures/override-value/source.js')
+    expect(result.code).to.be('\'use strict\';\n\nconsole.log(\'foo\');')
+  })
+
   it('should load default env from .env', function(){
     var result = babel.transformFileSync('test/fixtures/default/source.js')
     expect(result.code).to.be('\'use strict\';\n\nconsole.log(\'abc123\');\nconsole.log(\'username\');')

index.js

@@ -2,7 +2,7 @@ var path = require('path');
 
 module.exports = () => ({
   plugins: [
-    [require('babel-plugin-dotenv'), {
+    [require('./babel-plugin-dotenv'), {
       replacedModuleName: 'react-native-dotenv',
       configDir: path.resolve(__dirname, "../../")
     }],