diff --git a/src/arrays.js b/src/arrays.js
index f24d6ef..98f138c 100644
--- a/src/arrays.js
+++ b/src/arrays.js
@@ -6,33 +6,73 @@ 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 = [];
+  each(elements, (value) => {
+    arr.push(cb(value));
+  });
+  return arr;
 };
 
 const reduce = (elements, cb, memo) => {
   // 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 i = 0;
+  if (memo === undefined) {
+    memo = elements[0];
+    i = 1;
+  }
+  for (; i < elements.length; i++) {
+    memo = cb(memo, elements[i]);
+  }
+  return memo;
 };
 
 const find = (elements, cb) => {
   // 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.
+  for (let i = 0; i < elements.length; i++) {
+    if (cb(elements[i])) {
+      return elements[i];
+    }
+  }
+  return undefined;
 };
 
 const filter = (elements, cb) => {
   // 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
+  const newArr = [];
+  for (let i = 0; i < elements.length; i++) {
+    if (cb(elements[i])) {
+      newArr.push(elements[i]);
+    }
+  }
+  return newArr;
 };
 
 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 result = [];
+  each(elements, (elem) => {
+    if (Array.isArray(elem)) {
+      const nestedArray = flatten(elem);
+      result = result.concat(nestedArray);
+    } else {
+      result.push(elem);
+    }
+  });
+  return result;
 };
 
 /* eslint-enable no-unused-vars, max-len */
diff --git a/src/class.js b/src/class.js
index 8276e29..4ef5d75 100644
--- a/src/class.js
+++ b/src/class.js
@@ -5,7 +5,18 @@
 // 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.
-
+class User {
+  constructor(options) {
+    this.email = options.email;
+    this.password = options.password;
+  }
+  comparePasswords(potentialPassword) {
+    if (this.password === potentialPassword) {
+      return true;
+    }
+    return false;
+  }
+}
 
 /* eslint-disable no-undef */ // Remove this comment once you write your classes.
 
@@ -18,7 +29,24 @@
 // 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..a7def11 100644
--- a/src/closure.js
+++ b/src/closure.js
@@ -5,17 +5,42 @@ const counter = () => {
   // Example: const newCounter = counter();
   // newCounter(); // 1
   // newCounter(); // 2
+  let count = 0;
+  return () => {
+    count++;
+    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: () => {
+      count++;
+      return count;
+    },
+    decrement: () => {
+      count--;
+      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;
+  const returnFunction = (...args) => {
+    if (count === n) {
+      return null;
+    }
+    count++;
+    return cb(...args);
+  };
+  return returnFunction;
 };
 
 const cacheFunction = (cb) => {
@@ -25,6 +50,14 @@ 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 = {};
+  const cached = (arg) => {
+    if (Object.prototype.hasOwnProperty.call(cache, arg)) {
+      return cache[arg];
+    }
+    return cache[arg] = cb(arg);
+  };
+  return cached;
 };
 
 /* eslint-enable no-unused-vars */
diff --git a/src/es6.js b/src/es6.js
index eb846ab..ad7802e 100644
--- a/src/es6.js
+++ b/src/es6.js
@@ -7,18 +7,21 @@
 //----------------
 // const, =>, default parameters, arrow functions default return statements using ()
 
-var food = 'pineapple';
+/* 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';
 };
 
-var isThisMyFavorite = isMyFavoriteFood(food);
+/* 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;
@@ -34,23 +37,36 @@ var me = new User({
   username: username,
   password: password,
 });
+*/
 
+class User {
+  constructor(options) {
+    this.username = options.username;
+    this.password = options.password;
+  }
+  sayHi() {
+    return `${this.username} says hello!`;
+  }
+}
+
+const username = 'JavaScriptForever';
+const password = 'password';
 // ----------------
 // let, const, =>, ... (spread operator)
 
-var addArgs = function () {
-  var sum = 0;
-  for (var i = 0; i < arguments.length; i++) {
+let addArgs = function () {
+  let sum = 0;
+  for (let i = 0; i < arguments.length; i++) {
     sum += arguments[i];
   }
   return sum;
 };
 
-var argsToCb = function (cb) {
-  var args = Array.prototype.slice.call(arguments);
+let argsToCb = function (cb) {
+  let args = Array.prototype.slice.call(arguments);
   return cb.apply(null, args.splice(1));
 };
 
-var result = argsToCb(addArgs, 1, 2, 3, 4, 5); //result should be 15
+let 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..8292722 100644
--- a/src/objects.js
+++ b/src/objects.js
@@ -5,34 +5,61 @@ 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
+  const vals = Object.keys(obj).map((key) => {
+    return obj[key];
+  });
+  return vals;
 };
 
 const mapObject = (obj, cb) => {
   // Like map for arrays, but for objects. Transform the value of each property in turn.
   // http://underscorejs.org/#mapObject
+  Object.keys(obj).forEach(key => (obj[key] = cb(obj[key])));
+  return obj;
 };
 
 const pairs = (obj) => {
   // Convert an object into a list of [key, value] pairs.
   // http://underscorejs.org/#pairs
+  const keyValue = (Object.keys(obj).map(key => ([key, obj[key]])));
+  return keyValue;
 };
-
 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
+//  Object.keys(obj).forEach((key) => {
+//    const newKey = obj[key];
+//    obj[newKey] = key;
+//    delete obj[key];
+//  });
+//  return obj;
+  Object.keys(obj).forEach((key) => {
+    const newKey = obj[key];
+    obj[newKey] = key;
+    delete obj[key];
+  });
+  return obj;
 };
 
 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((key) => {
+    if (Object.prototype.hasOwnProperty.call(obj, key)) {
+      return;
+    }
+    obj[key] = defaultProps[key];
+  });
+  return obj;
 };
 
 /* eslint-enable no-unused-vars */
diff --git a/src/recursion.js b/src/recursion.js
index a3e997e..71f7421 100644
--- a/src/recursion.js
+++ b/src/recursion.js
@@ -3,11 +3,19 @@
 const nFibonacci = (n) => {
   // fibonacci sequence: 1 2 3 5 8 13 ...
   // return the nth number in the sequence
+  if (n === 0 || n === 1) {
+    return 1;
+  }
+  return nFibonacci(n - 1) + nFibonacci(n - 2);
 };
 
 const nFactorial = (n) => {
   // factorial example: !5 = 5 * 4 * 3 * 2 * 1
   // return the factorial of `n`
+  if (n === 0 || n === 1) {
+    return 1;
+  }
+  return n * (nFactorial(n - 1));
 };
 
 const checkMatchingLeaves = (obj) => {
diff --git a/src/this.js b/src/this.js
index 8ea3020..f60e4c0 100644
--- a/src/this.js
+++ b/src/this.js
@@ -5,10 +5,18 @@
 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(passwordCheck) {
+    if (this.password === passwordCheck) {
+      return true;
+    }
+    return false;
+  }
 }
 
 const me = new User({ username: 'LambdaSchool', password: 'correcthorsebatterystaple' });
@@ -19,13 +27,21 @@ 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 (this.password === passwordToCompare) {
+    return true;
+  }
+  return false;
 };
 
 // invoke `checkPassword` on `me` by explicitly setting the `this` context
 // use .call, .apply, and .bind
 
 // .call
+checkPassword.call(me, 'correcthorsebatterystaple');
 
 // .apply
+checkPassword.apply(me, ['correcthorsebatterystaple']);
 
 // .bind
+const boundPasswordCheck = checkPassword.bind(me);
+boundPasswordCheck('correcthorsebatterystaple');