feat: support es modules without .mjs extension

lib/index.js

@@ -17,16 +17,8 @@ var libfs       = require('fs'),
     libcache    = require('./cache'),
     deepFreeze  = require('deep-freeze'),
     promisify   = require('util').promisify,
-    mjs         = require('./mjs'),
-
-    MESSAGES = {
-        'unknown bundle': 'Unknown bundle "%s"',
-        'unknown config': 'Unknown config "%s" in bundle "%s"',
-        'unknown cache data': 'Unknown cache data with config "%s" in bundle "%s"',
-        'missing dimensions': 'Failed to find a dimensions.json file',
-        'parse error': 'Failed to parse "%s"\n%s',
-        'missing time': 'No time dimension, %s, in context, %s, during time aware mode'
-    },
+    loadModule  = require('./mod'),
+    MESSAGES    = require('./messages'),
     DEFAULT_CACHE_OPTIONS = {
         max: 250
     };
@@ -35,37 +27,6 @@ function clone(o) {
     return JSON.parse(JSON.stringify(o));
 }
 
-/**
- * Require the export of a CJS module or default export of a transpiled ESModule
- * @param {String} id module name or path
- * @returns {*} exported module content
- */
-function interopRequireDefault(id) {
-    var obj = require(id);
-    if (obj.__esModule) {
-        return obj.default;
-    }
-    return obj;
-}
-
-/**
- * Import an untranspiled ES Module
- * @param {String} id module name or path
- * @param {Function} [callback] Called once the config has been added to the helper.
- *   @param {Error|null} callback.err If an error occurred, then this parameter will
- *   contain the error. If the operation succeeded, then `err` will be null.
- *   @param {Object} callback.contents The contents of the config file, as a
- *   JavaScript object.
- */
-function importMjs(id, callback) {
-    mjs(id, function (err, obj) {
-        if (err) {
-            return callback(new Error(util.format(MESSAGES['parse error'], id, err.message)));
-        }
-        callback(null, obj.default);
-    });
-}
-
 function mix(target, source, overwrite) {
     var prop;
     for (prop in source) {
@@ -644,16 +605,8 @@ Config.prototype = {
                     return callback(err, contents);
                 });
             });
-        } else if (ext === '.mjs') {
-            return importMjs(path, callback);
-        } else {
-            try {
-                contents = interopRequireDefault(path);
-            } catch (e) {
-                return callback(new Error(util.format(MESSAGES['parse error'], path, e.message)));
-            }
-
-            return callback(null, contents);
+        } else  {
+            return loadModule(path, callback);
         }
     },
 
@@ -669,10 +622,8 @@ Config.prototype = {
                     contents = JSON.parse(contents);
                 } else if ('.json5' === ext) {
                     contents = libjson5.parse(contents);
-                } else if ('.mjs' === ext) {
-                    return importMjs(path, callback);
-                } else if ('.js' === ext) {
-                    contents = interopRequireDefault(path);
+                } else if ('.mjs' === ext || '.js' === ext) {
+                    return loadModule(path, callback);
                 } else {
                     contents = libyaml.parse(contents);
                 }

lib/messages.js

@@ -0,0 +1,8 @@
+module.exports = {
+    'unknown bundle': 'Unknown bundle "%s"',
+    'unknown config': 'Unknown config "%s" in bundle "%s"',
+    'unknown cache data': 'Unknown cache data with config "%s" in bundle "%s"',
+    'missing dimensions': 'Failed to find a dimensions.json file',
+    'parse error': 'Failed to parse "%s"\n%s',
+    'missing time': 'No time dimension, %s, in context, %s, during time aware mode'
+};

lib/mod/legacy.js

@@ -0,0 +1,19 @@
+var utils = require('./utils');
+
+/**
+ * Import a CommonJS config
+ * @param {String} id module name or path
+ * @param {Function} [callback] Called once the config has been added to the helper.
+ *   @param {Error|null} callback.err If an error occurred, then this parameter will
+ *   contain the error. If the operation succeeded, then `err` will be null.
+ *   @param {Object} callback.contents The contents of the config file, as a
+ *   JavaScript object.
+ */
+module.exports = function(id, callback) {
+    try {
+        var mod = utils.interopDefault(require(id));
+        callback(null, mod);
+    } catch (e) {
+        callback(new utils.ParseError(e, id));
+    }
+}

lib/mod/modern.js

@@ -0,0 +1,19 @@
+const { interopDefault, ParseError } = require('./utils');
+
+/**
+ * Import an ESModule config.
+ * @param {String} id module name or path
+ * @param {Function} [callback] Called once the config has been added to the helper.
+ *   @param {Error|null} callback.err If an error occurred, then this parameter will
+ *   contain the error. If the operation succeeded, then `err` will be null.
+ *   @param {Object} callback.contents The contents of the config file, as a
+ *   JavaScript object.
+ */
+module.exports = async (id, callback) => {
+    try {
+        const mod = interopDefault(await import(id));
+        callback(null, mod.default);
+    } catch (e) {
+        callback(new ParseError(e, id));
+    }
+}

lib/mod/utils.js

@@ -0,0 +1,23 @@
+var MESSAGES = require('../messages');
+var util = require('util');
+
+/**
+ * Return the export of a CJS module or default export of a transpiled ESModule
+ * See https://babeljs.io/docs/en/babel-plugin-transform-modules-commonjs
+ * @param {Object} mod module
+ * @returns {*} exported module content
+ */
+module.exports.interopDefault = function interopDefault(mod) {
+    if (mod && mod.__esModule) {
+        return mod.default;
+    }
+    return mod;
+}
+
+module.exports.ParseError = (function () {
+    function ParseError(e, id) {
+        this.message = util.format(MESSAGES['parse error'], id, e.message)
+    }
+    ParseError.prototype = new Error;
+    return ParseError;
+})();

package.json

@@ -1,6 +1,6 @@
 {
     "name": "ycb-config",
-    "version": "2.2.0",
+    "version": "2.3.0",
     "description": "Configuration manager for Yahoo configuration bundles",
     "author": "Drew Folta <folta@yahoo-inc.com>",
     "contributors": [],

tests/lib/index.js

@@ -360,8 +360,8 @@ describe('config', function () {
                             next(err);
                         }
                     } else {
-                        expect(err).to.be.an('error');
-                        expect(err.message).to.include('Node >= 12 is required to import .mjs file');
+                        expect(err).to.be.an.instanceof(Error);
+                        expect(err.message).to.include('Unexpected token export');
                         next();
                     }
                 });