paulghaddad · paulghaddad · Feb 22, 2018 · Feb 22, 2018 · Feb 22, 2018 · Feb 23, 2018
diff --git a/src/arrays.js b/src/arrays.js
@@ -14,12 +14,22 @@ 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) => {
   // Do NOT use .map, to complete this function.
   // Produces a new array of values by mapping each value in list through a transformation function (iteratee).
   // Return the new array.
+  let mappedArray = [];
+
+  elements.forEach((el) => {
+    return mappedArray = [...mappedArray, cb(el)];
+  });
+
+  return mappedArray;
 };
 
 const reduce = (elements, cb, startingValue) => {
@@ -28,26 +38,67 @@ const reduce = (elements, cb, startingValue) => {
   // Elements will be passed one by one into `cb` along with the `startingValue`.
   // `startingValue` should be the first argument passed to `cb` and the array element should be the second argument.
   // `startingValue` is the starting value.  If `startingValue` is undefined then make `elements[0]` the initial value.
+  let reducedValue = startingValue || elements[0];
+  const startingIndex = (startingValue !== undefined) ? 0 : 1;
+
+  for (let i = startingIndex; i < elements.length; i++) {
+    reducedValue = cb(reducedValue, elements[i]);
+  }
+
+  return reducedValue;
 };
 
 const find = (elements, cb) => {
   // Do NOT use .includes, to complete this function.
   // 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++) {
+    const element = elements[i];
+
+    if (cb(element)) {
+      return element;
+    }
+  }
+
+  return false;
 };
 
 const filter = (elements, cb) => {
   // Do NOT use .filter, to complete this function.
   // 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
+  let filteredElements = [];
+
+  for (let i = 0; i < elements.length; i++) {
+    const element = elements[i];
+
+    if (cb(element)) {
+      filteredElements = [...filteredElements, element];
+    }
+  }
+
+  return filteredElements;
 };
 
 /* STRETCH PROBLEM */
 
 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 flattenedElements = [];
+
+  for (let i = 0; i < elements.length; i++) {
+    const element = elements[i];
+
+    if (Array.isArray(element)) {
+      flattenedElements = flatten([...flattenedElements, element[0]]);
+    } else {
+      flattenedElements = [...flattenedElements, element];
+    }
+  }
+
+  return flattenedElements;
 };
 
 /* eslint-enable no-unused-vars, max-len */

diff --git a/src/callbacks.js b/src/callbacks.js
@@ -1,26 +1,35 @@
 const firstItem = (arr, cb) => {
   // firstItem passes the first item of the given array to the callback function.
+  cb(arr[0]);
 };
 
 const getLength = (arr, cb) => {
   // getLength passes the length of the array into the callback.
+  cb(arr.length);
 };
 
 const last = (arr, cb) => {
   // last passes the last item of the array into the callback.
+  cb(arr[arr.length - 1]);
 };
 
 const sumNums = (x, y, cb) => {
   // sumNums adds two numbers (x, y) and passes the result to the callback.
+  const sum = x + y;
+  cb(sum);
 };
 
 const multiplyNums = (x, y, cb) => {
   // multiplyNums multiplies two numbers and passes the result to the callback.
+  const product = x * y;
+  cb(product);
 };
 
 const contains = (item, list, cb) => {
   // contains checks if an item is present inside of the given array/list.
   // Pass true to the callback if it is, otherwise pass false.
+  const itemPresent = list.includes(item);
+  cb(itemPresent);
 };
 
 /* STRETCH PROBLEM */
@@ -29,6 +38,8 @@ const removeDuplicates = (array, cb) => {
   // removeDuplicates removes all duplicate values from the given array.
   // Pass the duplicate free array to the callback function.
   // Do not mutate the original array.
+  const uniqueElements = new Set(array);
+  cb(Array.from(uniqueElements));
 };
 
 /* eslint-enable */

diff --git a/src/closure.js b/src/closure.js
@@ -5,17 +5,46 @@ const counter = () => {
   // Example: const newCounter = counter();
   // newCounter(); // 1
   // newCounter(); // 2
+  let count = 0;
+
+  function incrementCount() {
+    return count += 1;
+  }
+
+  return incrementCount;
 };
 
 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;
+
+  const increment = () => count += 1;
+  const decrement = () => count -= 1;
+
+  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 count = 0;
+
+  const invokeCb = (...options) => {
+    if (count < n) {
+      count += 1;
+      return cb(...options);
+    }
+
+    return null;
+  };
+
+  return invokeCb;
 };
 
 /* STRETCH PROBLEM */
@@ -27,6 +56,22 @@ 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 invokeCb = (...options) => {
+    const argument = options[0];
+
+    if (Object.prototype.hasOwnProperty.call(cache, argument)) {
+      return cache[argument];
+    }
+
+    const result = cb(argument);
+    cache[argument] = result;
+    return result;
+  };
+
+  return invokeCb;
 };
 
 /* eslint-enable no-unused-vars */

diff --git a/src/objects.js b/src/objects.js
@@ -5,36 +5,75 @@ 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 objectKeys = Object.keys(obj);
+
+  for (let i = 0; i < objectKeys.length; i++) {
+    const key = objectKeys[i];
+    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 objectKeys = Object.keys(obj);
+  let keyValuePairs = [];
+
+  for (let i = 0; i < objectKeys.length; i++) {
+    const key = objectKeys[i];
+    keyValuePairs = [...keyValuePairs, [key, obj[key]]];
+  }
+
+  return keyValuePairs;
 };
 
 /* STRETCH PROBLEMS */
-
 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 objectKeys = Object.keys(obj);
+  let invertedObject = {};
+
+  for (let i = 0; i < objectKeys.length; i++) {
+    const key = objectKeys[i];
+    const value = obj[key];
+    invertedObject[value] = key;
+  }
+
+  return invertedObject;
 };
 
 const defaults = (obj, defaultProps) => {
   // Fill in undefined properties that match properties on the `defaultProps` parameter object.
   // Return `obj`.
   // http://underscorejs.org/#defaults
+  const defaultKeys = Object.keys(defaultProps);
+
+  for (let i = 0; i < defaultKeys.length; i++) {
+    const defaultKey = defaultKeys[i];
+
+    if (!obj.hasOwnProperty(defaultKey)) {
+      obj[defaultKey] = defaultProps[defaultKey];
+    }
+  }
+
+  return obj;
 };
 
 /* eslint-enable no-unused-vars */

diff --git a/tests/arrays.test.js b/tests/arrays.test.js
@@ -103,6 +103,7 @@ describe('arrays', () => {
       const arr = [1, 2, 3, 4, 5];
       const results = arrayMethods.flatten(arr);
       expect(Array.isArray(results)).toBe(true);
+      expect(results).toEqual([1, 2, 3, 4, 5]);
     });
     it('should return a flattened array when given a nested array', () => {
       const arr = [1, 2, 3, 4, 5, [6], [7]];