Change the index file format to use "export ... from" (fixes #3)

src/utilities/writeIndex.js

@@ -0,0 +1,31 @@
+import _ from 'lodash';
+import createIndexCode from './createIndexCode';
+import fs from 'fs';
+import path from 'path';
+import validateTargetDirectory from './validateTargetDirectory';
+import readDirectory from './readDirectory';
+import sortByDepth from './sortByDepth';
+
+export default (directoryPaths) => {
+    let sortedDirectoryPaths;
+
+    sortedDirectoryPaths = sortByDepth(directoryPaths);
+
+    _.forEach(sortedDirectoryPaths, (directoryPath) => {
+        validateTargetDirectory(directoryPath);
+    });
+
+    _.forEach(sortedDirectoryPaths, (directoryPath) => {
+        let indexCode,
+            indexFilePath,
+            siblings;
+
+        siblings = readDirectory(directoryPath);
+
+        indexCode = createIndexCode(siblings);
+
+        indexFilePath = path.resolve(directoryPath, 'index.js');
+
+        fs.writeFileSync(indexFilePath, indexCode);
+    });
+};