@@ -1,47 +1,69 @@
-// Complete the following underscore functions.
-// Reference http://underscorejs.org/ for examples.
-
-const keys = (obj) => {
-  // Retrieve all the names of the object's properties.
-  // Return the keys as strings in an array.
-  // Based on http://underscorejs.org/#keys
-};
-
-const values = (obj) => {
-  // Return all of the values of the object's own properties.
-  // Ignore functions
-  // http://underscorejs.org/#values
-};
-
-const mapObject = (obj, cb) => {
-  // Like map for arrays, but for objects. Transform the value of each property in turn.
-  // http://underscorejs.org/#mapObject
-};
-
-const pairs = (obj) => {
-  // Convert an object into a list of [key, value] pairs.
-  // http://underscorejs.org/#pairs
-};
-
-const invert = (obj) => {
-  // Returns a copy of the object where the keys have become the values and the values the keys.
-  // Assume that all of the object's values will be unique and string serializable.
-  // http://underscorejs.org/#invert
-};
-
-const defaults = (obj, defaultProps) => {
-  // Fill in undefined properties that match properties on the `defaultProps` parameter object.
-  // Return `obj`.
-  // http://underscorejs.org/#defaults
-};
-
-/* eslint-enable no-unused-vars */
-
-module.exports = {
-  keys,
-  values,
-  mapObject,
-  pairs,
-  invert,
-  defaults
-};
+// Complete the following underscore functions.
+// Reference http://underscorejs.org/ for examples.
+
+const keys = (obj) => {
+  // Retrieve all the names of the object's properties.
+  // Return the keys as strings in an array.
+  // Based on http://underscorejs.org/#keys
+  return Object.keys(obj);
+};
+
+const values = (obj) => {
+  // Return all of the values of the object's own properties.
+  // Ignore functions
+  // http://underscorejs.org/#values
+  return Object.values(obj);
+};
+
+const mapObject = (obj, cb) => {
+  // Like map for arrays, but for objects. Transform the value of each property in turn.
+  // http://underscorejs.org/#mapObject
+  const keyArr = Object.keys(obj);
+  const result = {};
+
+  keyArr.forEach((k) => {
+    result[k] = cb(obj[k]);
+  });
+  return result;
+};
+
+const pairs = (obj) => {
+  // Convert an object into a list of [key, value] pairs.
+  // http://underscorejs.org/#pairs
+  return Object.entries(obj);
+};
+
+const invert = (obj) => {
+  // Returns a copy of the object where the keys have become the values and the values the keys.
+  // Assume that all of the object's values will be unique and string serializable.
+  // http://underscorejs.org/#invert
+  const keyArr = Object.keys(obj);
+  const result = {};
+
+  keyArr.forEach(k => result[obj[k]] = k);
+  return result;
+};
+
+const defaults = (obj, defaultProps) => {
+  // Fill in undefined properties that match properties on the `defaultProps` parameter object.
+  // Return `obj`.
+  // http://underscorejs.org/#defaults
+  const keyArr = Object.keys(defaultProps);
+  keyArr.forEach((k) => {
+    if (!obj[k]) {
+      obj[k] = defaultProps[k];
+    }
+  });
+  return obj;
+};
+
+/* eslint-enable no-unused-vars */
+
+module.exports = {
+  keys,
+  values,
+  mapObject,
+  pairs,
+  invert,
+  defaults
+};