diff --git a/.eslintrc.json b/.eslintrc.json
index 08aceb1a..1f7daf68 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -17,4 +17,4 @@
       "no-useless-constructor": 0,
       "import/no-unresolved": 0
     }
-}
+}
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index c3c1388e..8eb72412 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 *.swp
 node_modules
+package-lock.json
+*yarn*
diff --git a/src/arrays.js b/src/arrays.js
index af8d60eb..dcef359e 100644
--- a/src/arrays.js
+++ b/src/arrays.js
@@ -9,37 +9,89 @@ const each = (elements, cb) => {
   // This only needs to work with arrays.
   // You should also pass the index into `cb` as the second argument
   // 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 reduce = (elements, cb, startingValue) => {
   // Combine all elements into a single value going from left to right.
   // Elements will be passed one by one into `cb`.
   // `startingValue` is the starting value.  If `startingValue` is undefined then make `elements[0]` the initial value.
+  let i = 0;
+  if (startingValue === undefined) {
+    startingValue = elements[0];
+    i = 1;
+  }
+  let acc = startingValue;
+  for (; i < elements.length; i++) {
+    acc = cb(acc, elements[i], i);
+  }
+  return acc;
+};
+
+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.
+  return reduce(elements, (acc, v) => {
+    acc.push(cb(v));
+    return acc;
+  }, []);
 };
 
 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
+  return reduce(elements, (acc, v) => {
+    if (cb(v)) {
+      acc.push(v);
+    }
+    return acc;
+  }, []);
 };
 
 /* Extra Credit */
-
+const isArray = (elements) => {
+  return Array.isArray(elements);
+};
 const flatten = (elements) => {
   // Flattens a nested array (the nesting can be to any depth).
   // Example: flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4];
+  if (!isArray(elements)) {
+    return elements;
+  }
+  while (elements.length === 1 && Array.isArray(elements[0])) {
+    elements = elements[0];
+  }
+  let r = [];
+  r.push(flatten(elements[0]));
+  let next = elements.slice(1);
+  while (next.length === 1 && Array.isArray(next[0])) {
+    next = next[0];
+  }
+  if (next.length > 0) {
+    while (r.length === 1 && Array.isArray(r[0])) {
+      r = r[0];
+    }
+    r = r.concat(flatten(next));
+  }
+  return r;
 };
 
+
 /* eslint-enable no-unused-vars, max-len */
 
 module.exports = {
diff --git a/src/callbacks.js b/src/callbacks.js
index c0c44a74..e043ec01 100644
--- a/src/callbacks.js
+++ b/src/callbacks.js
@@ -25,34 +25,46 @@
 
 const foods = ['pineapple', 'mango', 'ribeye', 'curry', 'tacos', 'ribeye', 'mango'];
 
+function firstItem(foods, f) {
+  return f(foods[0]);
+}
+
 firstItem(foods, (firstItem) => {
   console.log(`The first item is ${firstItem}.`);
 });
 
 // Write a function called getLength that passes the length of the array into the callback
 // code here
-
+function getLength(foods, f) {
+  return f(foods.length);
+}
 getLength(foods, (length) => {
   console.log(`The length of the array is ${length}.`);
 });
 
 // Write a function called last which passes the last item of the array into the callback
 // code here
-
+function last(foods, f) {
+  return f(foods[foods.length -1]);
+}
 last(foods, (lastItem) => {
   console.log(`The last item in the array is ${lastItem}.`);
 });
 
 // Write a function called sumNums that adds two numbers and passes the result to the callback
 // code here
-
+function sumNums(x, y, f) {
+  return f(x + y)
+}
 sumNums(5, 10, (sum) => {
   console.log(`The sum is ${sum}.`);
 });
 
 // Write a function called multiplyNums that adds two numbers and passes the result to the callback
 // code here
-
+function multiplyNums(x, y, f) {
+  return f(x * y);
+}
 multiplyNums(5, 10, (product) => {
   console.log(`The product is ${product}.`);
 });
@@ -60,7 +72,9 @@ multiplyNums(5, 10, (product) => {
 // Write a function called contains that checks if an item is present inside of the given array.
 // Pass true to the callback if it is, otherwise pass false
 // code here
-
+function contains(foods, item, f) {
+  return f(foods.indexOf(item) >= 0)
+}
 contains(foods, 'ribeye', (result) => {
   console.log(result ? 'ribeye is in the array' : 'ribeye is not in the array');
 });
@@ -68,14 +82,20 @@ contains(foods, 'ribeye', (result) => {
 // Write a function called removeDuplicates that removes all duplicate values from the given array.
 // Pass the array to the callback function.  Do not mutate the original array.
 // code here
-
+function removeDuplicates(foods, f) {
+  f(foods.filter((food,i) => {
+    return foods.indexOf(food) === i;
+  }))
+}
 removeDuplicates(foods, (uniqueFoods) => {
   console.log(`foods with duplicates removed: ${uniqueFoods}`);
 });
 
 // Write a function called forEach that iterates over the provided array and passes the value and index into the callback.
 // code here
-
+function forEach(foods, f) {
+  return foods.forEach((food,i) => f(food,i));
+}
 forEach(foods, (value, index) => {
   console.log(`${value} is at index ${index}.`);
 });
diff --git a/src/closure.js b/src/closure.js
index 4ba806c3..fbc88053 100644
--- a/src/closure.js
+++ b/src/closure.js
@@ -5,17 +5,39 @@ const counter = () => {
   // Example: const newCounter = counter();
   // newCounter(); // 1
   // newCounter(); // 2
+  let localCounter = 0;
+  return () => {
+    return ++localCounter;
+  };
 };
 
 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 closureCounter = 0;
+  const increment = () => {
+    return ++closureCounter;
+  };
+  const decrement = () => {
+    return --closureCounter;
+  };
+  return {
+    increment,
+    decrement,
+  };
 };
 
 const limitFunctionCallCount = (cb, n) => {
   // Should return a function that invokes `cb`.
   // The returned function should only allow `cb` to be invoked `n` times.
+  let times = 0;
+  return (...args) => {
+    if (++times <= n) {
+      return cb(...args);
+    }
+    return null;
+  };
 };
 
 /* Extra Credit */
@@ -27,6 +49,17 @@ 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) => {
+    let result;
+    if (!(args.toString() in cache)) {
+      result = cb(...args);
+      cache[args.toString()] = result;
+    } else {
+      result = cache[args.toString()];
+    }
+    return result;
+  };
 };
 
 /* eslint-enable no-unused-vars */
diff --git a/src/objects.js b/src/objects.js
index fbc37b91..b314a820 100644
--- a/src/objects.js
+++ b/src/objects.js
@@ -1,26 +1,47 @@
 // Complete the following underscore functions.
 // Reference http://underscorejs.org/ for examples.
+const each = require('./arrays.js').each;
 
 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);
 };
-
+function isFunction(func) {
+  return (typeof func === 'function');
+}
 const values = (obj) => {
   // Return all of the values of the object's own properties.
   // Ignore functions
   // http://underscorejs.org/#values
+  const r = [];
+  each(keys(obj), (key) => {
+    if (!isFunction(obj[key])) {
+      r.push(obj[key]);
+    }
+  });
+  return r;
 };
 
 const mapObject = (obj, cb) => {
   // Like map for arrays, but for objects. Transform the value of each property in turn.
   // http://underscorejs.org/#mapObject
+  const r = {};
+  each(keys(obj), (key) => {
+    r[key] = cb(obj[key]);
+  });
+  return r;
 };
 
 const pairs = (obj) => {
   // Convert an object into a list of [key, value] pairs.
   // http://underscorejs.org/#pairs
+  const r = [];
+  each(keys(obj), (key) => {
+    r.push([key, obj[key]]);
+  });
+  return r;
 };
 
 /* Extra credit */
@@ -29,12 +50,23 @@ 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 r = {};
+  each(keys(obj), (key) => {
+    r[obj[key]] = key;
+  });
+  return r;
 };
 
 const defaults = (obj, defaultProps) => {
   // Fill in undefined properties that match properties on the `defaultProps` parameter object.
   // Return `obj`.
   // http://underscorejs.org/#defaults
+  each(keys(defaultProps), (key) => {
+    if (obj[key] === undefined) {
+      obj[key] = defaultProps[key];
+    }
+  });
+  return obj;
 };
 
 /* eslint-enable no-unused-vars */