diff --git a/src/arrays.js b/src/arrays.js
index 26aaed3..75dd384 100644
--- a/src/arrays.js
+++ b/src/arrays.js
@@ -8,26 +8,47 @@ const each = (elements, cb) => {
   // Iterates over a list of elements, yielding each in turn to the `cb` function.
   // This only needs to work with arrays.
   // based off http://underscorejs.org/#each
+  for (let i = 0; i < elements.length; i++) {
+    cb(elements[i], i);
+  }
 };
 
 const map = (elements, cb) => {
   // Produces a new array of values by mapping each value in list through a transformation function (iteratee).
   // Return the new array.
+  const arr = [];
+  for (let i = 0; i < elements.length; i++) {
+    arr.push(cb(elements[i]));
+  }
+  return arr;
 };
 
 const reduce = (elements, cb, memo = elements.shift()) => {
   // Combine all elements into a single value going from left to right.
   // Elements will be passed one by one into `cb`.
   // `memo` is the starting value.  If `memo` is undefined then make `elements[0]` the initial value.
+  let result = memo;
+  for (let i = 0; i < elements.length; i++) {
+    result = cb(result, elements[i]);
+  }
+  return result;
 };
 
 const find = (elements, cb) => {
+  for (let i = 0; i < elements.length; i++) {
+    if (cb(elements[i]) === true) return elements[i];
+  }
   // Look through each value in `elements` and pass each element to `cb`.
   // If `cb` returns `true` then return that element.
   // Return `undefined` if no elements pass the truth test.
 };
 
 const filter = (elements, cb) => {
+  const array = [];
+  for (let i = 0; i < elements.length; i++) {
+    if (cb(elements[i]) === true) array.push(elements[i]);
+  }
+  return array;
   // Similar to `find` but you will return an array of all elements that passed the truth test
   // Return an empty array if no elements pass the truth test
 };
@@ -35,6 +56,12 @@ const filter = (elements, cb) => {
 const flatten = (elements) => {
   // Flattens a nested array (the nesting can be to any depth).
   // Example: flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4];
+  let array = [];
+  for (let i = 0; i < elements.length; i++) {
+    const roller = Array.isArray(elements[i]) ? flatten(elements[i]) : [elements[i]];
+    array = array.concat(roller);
+  }
+  return array;
 };
 
 /* eslint-enable no-unused-vars, max-len */
diff --git a/src/class.js b/src/class.js
index 8276e29..aee07ae 100644
--- a/src/class.js
+++ b/src/class.js
@@ -5,9 +5,16 @@
 // Add a method called `comparePasswords`.  `comparePasswords` should have a parameter
 // for a potential password that will be compared to the `password` property.
 // Return true if the potential password matches the `password` property.  Otherwise return false.
-
-
-/* eslint-disable no-undef */ // Remove this comment once you write your classes.
+class User {
+  constructor(options) {
+    this.email = options.email;
+    this.password = options.password;
+  }
+  comparePasswords(str) {
+    if (str === this.password) return true;
+    return false;
+  }
+}
 
 
 // Create a class called `Animal` and a class called `Cat`.
@@ -18,7 +25,20 @@
 // Cat should have the property `name` that is set in the constructor and the method
 // `meow` that should return the string `<name> meowed!` where `<name>` is the `name`
 // property set on the Cat instance.
+class Animal {
+  constructor(options) {
+    this.age = options.age;
+  }
+  growOlder() { return this.age + 1; }
+}
 
+class Cat extends Animal {
+  constructor(options) {
+    super(options);
+    this.name = options.name;
+  }
+  meow() { return `${this.name} meowed!`; }
+}
 
 module.exports = {
   User,
diff --git a/src/closure.js b/src/closure.js
index 4c98af0..16df815 100644
--- a/src/closure.js
+++ b/src/closure.js
@@ -5,17 +5,29 @@ const counter = () => {
   // Example: const newCounter = counter();
   // newCounter(); // 1
   // newCounter(); // 2
+  let count = 0;
+  return () => ++count;
 };
 
 const counterFactory = () => {
   // Return an object that has two methods called `increment` and `decrement`.
   // `increment` should increment a counter variable in closure scope and return it.
   // `decrement` should decrement the counter variable and return it.
+  let count = 0;
+  return {
+    increment() { return ++count; },
+    decrement() { return --count; }
+  };
 };
 
 const limitFunctionCallCount = (cb, n) => {
   // Should return a function that invokes `cb`.
   // The returned function should only allow `cb` to be invoked `n` times.
+  let count = 0;
+  return (...args) => {
+    if (count < n) { count++; return cb(...args); }
+    return null;
+  };
 };
 
 const cacheFunction = (cb) => {
@@ -25,8 +37,13 @@ const cacheFunction = (cb) => {
   // If the returned function is invoked with arguments that it has already seen
   // then it should return the cached result and not invoke `cb` again.
   // `cb` should only ever be invoked once for a given set of arguments.
+  const cache = [];
+  return (...args) => {
+    if (cache.includes(...args)) return cache;
+    cache.push(...args);
+    return cb(...args);
+  };
 };
-
 /* eslint-enable no-unused-vars */
 
 module.exports = {
diff --git a/src/es6.js b/src/es6.js
index eb846ab..9c8aa07 100644
--- a/src/es6.js
+++ b/src/es6.js
@@ -7,50 +7,40 @@
 //----------------
 // const, =>, default parameters, arrow functions default return statements using ()
 
-var food = 'pineapple';
+const food = 'pineapple';
 
-var isMyFavoriteFood = function(food) {
-  food = food || 'thousand-year-old egg'; //This sets a default value if `food` is falsey
-  return food === 'thousand-year-old egg';
-};
+const isMyFavoriteFood = (food = 'thousand-year-old egg') => (food === 'thousand-year-old egg'); //This sets a default value if `food` is falsey
 
-var isThisMyFavorite = isMyFavoriteFood(food);
+const isThisMyFavorite = isMyFavoriteFood(food);
 
 //----------------
 //const, class, template literals, enhanced object literals (foo: foo, -> foo,)
 
-var User = function(options) {
-  this.username = options.username;
-  this.password = options.password;
-  this.sayHi = function() {
-    return this.username + ' says hello!';
-  };
+class User {
+ constructor(options) {
+ 	this.username = options.username;
+	this.password = options.password;
+ }
+  sayHi() {
+		return `${this.username} says hello!`
+	}
 }
 
-var username = 'JavaScriptForever';
-var password = 'password';
+const username = 'JavaScriptForever';
+const password = 'password';
 
-var me = new User({
-  username: username,
-  password: password,
+const me = new User({
+  username,
+  password,
 });
 
 // ----------------
 // let, const, =>, ... (spread operator)
 
-var addArgs = function () {
-  var sum = 0;
-  for (var i = 0; i < arguments.length; i++) {
-    sum += arguments[i];
-  }
-  return sum;
-};
+const addArgs = (...args) => (args.reduce((memo, val) => (memo + val)));
 
-var argsToCb = function (cb) {
-  var args = Array.prototype.slice.call(arguments);
-  return cb.apply(null, args.splice(1));
-};
+const argsToCb = (cb, ...args) => (cb(...args));
 
-var result = argsToCb(addArgs, 1, 2, 3, 4, 5); //result should be 15
+const result = argsToCb(addArgs, 1, 2, 3, 4, 5); //result should be 15
 
 /* eslint-enable */
diff --git a/src/objects.js b/src/objects.js
index ba39c6c..9319f96 100644
--- a/src/objects.js
+++ b/src/objects.js
@@ -5,34 +5,46 @@ 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
+  keys(obj).forEach(k => obj[k] = cb(obj[k]));
+  return obj;
 };
 
 const pairs = (obj) => {
   // Convert an object into a list of [key, value] pairs.
   // http://underscorejs.org/#pairs
+  const array = [];
+  keys(obj).forEach(k => array.push([k, obj[k]]));
+  return array;
 };
 
 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 inv = {};
+  keys(obj).forEach(k => inv[obj[k]] = k);
+  return inv;
 };
 
 const defaults = (obj, defaultProps) => {
   // Fill in undefined properties that match properties on the `defaultProps` parameter object.
   // Return `obj`.
   // http://underscorejs.org/#defaults
+  Object.keys(defaultProps).forEach((d) => { if (!obj[d]) obj[d] = defaultProps[d]; });
+  return obj;
 };
 
 /* eslint-enable no-unused-vars */
diff --git a/src/recursion.js b/src/recursion.js
index a3e997e..50ffd7d 100644
--- a/src/recursion.js
+++ b/src/recursion.js
@@ -3,16 +3,26 @@
 const nFibonacci = (n) => {
   // fibonacci sequence: 1 2 3 5 8 13 ...
   // return the nth number in the sequence
+  return n <= 1 ? 1 : nFibonacci(n - 1) + nFibonacci(n - 2);
 };
 
 const nFactorial = (n) => {
   // factorial example: !5 = 5 * 4 * 3 * 2 * 1
   // return the factorial of `n`
+  return n <= 1 ? 1 : n * nFactorial(n - 1);
 };
 
 const checkMatchingLeaves = (obj) => {
   // return true if every property on `obj` is the same
   // otherwise return false
+  const array = [];
+  const rf = (...args) => {
+    Object.values(...args).forEach((v) => {
+      return typeof v === 'object' ? rf(v) : array.push(v);
+    });
+  };
+  rf(obj);
+  return new Set(array).size === 1;
 };
 
 /* eslint-enable no-unused-vars */
diff --git a/src/this.js b/src/this.js
index 8ea3020..1023b5b 100644
--- a/src/this.js
+++ b/src/this.js
@@ -5,10 +5,16 @@
 class User {
   constructor(options) {
     // set a username and password property on the user object that is created
+    this.username = options.username;
+    this.password = options.password;
   }
   // create a method on the User class called `checkPassword`
   // this method should take in a string and compare it to the object's password property
   // return `true` if they match, otherwise return `false`
+  checkPassword(str) {
+    if (str === this.password) return true;
+    return false;
+  }
 }
 
 const me = new User({ username: 'LambdaSchool', password: 'correcthorsebatterystaple' });
@@ -19,13 +25,16 @@ const checkPassword = function comparePasswords(passwordToCompare) {
   // use `this` to access the object's `password` property.
   // do not modify this function's parameters
   // note that we use the `function` keyword and not `=>`
+  if (passwordToCompare === this.password) return true;
+  return false;
 };
 
 // invoke `checkPassword` on `me` by explicitly setting the `this` context
 // use .call, .apply, and .bind
-
+checkPassword.call(me, this.password);
 // .call
-
+checkPassword.apply(me, [this.password]);
 // .apply
-
+const checkMyPassword = checkPassword.bind(me);
+checkMyPassword(this.password);
 // .bind