JavaScript 1 Challenge (Closure)

package.json

@@ -27,6 +27,7 @@
     "regenerator-runtime": "^0.10.3"
   },
   "dependencies": {
-    "eslint-config-airbnb": "^14.1.0"
+    "eslint-config-airbnb": "^14.1.0",
+    "yarn-install": "^0.5.1"
   }
 }

src/arrays.js

@@ -14,12 +14,26 @@ 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++) {
+    // pass each el and its index in the given array to a cb
+    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.
+
+  // hold transformed els into an array
+  const newArr = [];
+  for (let i = 0; i < elements.length; i++) {
+    // transform each el in the given array and push the result to newArr
+    newArr.push(cb(elements[i]));
+  }
+  // output: array containing the transformed els
+  return newArr;
 };
 
 const reduce = (elements, cb, startingValue) => {
@@ -28,27 +42,81 @@ 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.
+  // a holds either the starting value or the first el
+  let a;
+  if (startingValue) {
+    a = startingValue;
+  } else {
+    // if startingValue is falsy assign a to the first el of the given arr
+    a = elements.shift();
+  }
+  // copy the given arr
+  const sliced = elements.slice();
+  for (let i = 0; i < sliced.length; i++) {
+    // pass a and els of sliced into a cb
+    // set a to the result of the combining function
+    a = cb(a, sliced[i]);
+  }
+  // output: result of combining all the els in the given arr with cb
+  return a;
 };
 
 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++) {
+    // iterate over the given arr
+    if (cb(elements[i])) {
+      // only return elements for which cb return true
+      return elements[i];
+    }
+  }
 };
 
 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
+
+  // hold the els that pass the check in a new array
+  const result = [];
+  for (let i = 0; i < elements.length; i++) {
+    // check if the els pass the test in cb
+    if (cb(elements[i])) {
+      result.push(elements[i]);
+    }
+  }
+  // output: array that holds all elements that passed a test in cb
+  return result;
 };
 
 /* 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];
+  const flat = [];
+  function flattenArr(a) {
+      // base case: el in arr is not an array
+    if (!Array.isArray(a)) {
+      flat.push(a);
+    } else {
+      // recursive case: el is an array
+      // iterate over a: go one level into el
+      a.forEach(el => flattenArr(el));
+    }
+    return flat;
+  }
+  return flattenArr(elements);
 };
+// test cases courtesy of FreeCodeCamp
+  // https://www.freecodecamp.org/challenges/steamroller
+// flatten([1, [2], [3, [[4]]]]) returns [1, 2, 3, 4]
+// flatten([1, [], [3, [[4]]]]) returns [1, 3, 4]
+// flatten([[["a"]], [["b"]]]) returns ["a", "b"]
+// flatten([1, {}, [3, [[4]]]]) returns [1, {}, 3, 4]
 
 /* eslint-enable no-unused-vars, max-len */
 

src/callbacks.js

@@ -1,26 +1,34 @@
 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.
+  cb(x + y);
 };
 
 const multiplyNums = (x, y, cb) => {
   // multiplyNums multiplies two numbers and passes the result to the callback.
+  cb(x * y);
 };
 
 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.
+  // includes() returns true if item is in the given array
+  // else includes() returns false
+  cb(list.includes(item));
 };
 
 /* STRETCH PROBLEM */
@@ -29,6 +37,9 @@ 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.
+  // hold unique elements in a new array
+  const uniqueEls = Array.from(new Set(array));
+  return cb(uniqueEls);
 };
 
 /* eslint-enable */

src/closure.js

@@ -3,19 +3,52 @@
 const counter = () => {
   // Return a function that when invoked increments and returns a counter variable.
   // Example: const newCounter = counter();
-  // newCounter(); // 1
-  // newCounter(); // 2
+  // initialize a counter to 0
+  let count = 0;
+  function newCounter() {
+  // newCounter increments count by 1 at every function call
+    count++;
+    // count is updated and sent to counter scope
+    return count;
+  }
+  newCounter(); // 1
+  newCounter(); // 2
 };
 
 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.
+  // initialize a counter to 0
+  let count = 0;
+  // calculate obj holds increment and decrement functions
+  const calculate = {
+    increment() {
+    // add 1 to count
+      count++;
+      return count;
+    },
+    decrement() {
+    // subtract 1 from count
+      count--;
+      return count;
+    }
+  };
+  calculate.increment();
+  calculate.decrement();
 };
 
 const limitFunctionCallCount = (cb, n) => {
   // Should return a function that invokes `cb`.
   // The returned function should only allow `cb` to be invoked `n` times.
+  function limit() {
+  // while n is greater than 0 invoke cb
+    while (n > 0) {
+      cb();
+      n--;
+    }
+  }
+  return limit(cb);
 };
 
 /* STRETCH PROBLEM */
@@ -27,6 +60,7 @@ 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.
+
 };
 
 /* eslint-enable no-unused-vars */

src/objects.js

@@ -5,22 +5,35 @@ 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
+  // output: an array containing the properties of obj
+  return Object.keys(obj);
 };
 
 const values = (obj) => {
   // Return all of the values of the object's own properties.
   // Ignore functions
   // http://underscorejs.org/#values
+  // output: an array containing the values of obj
+  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 props = Object.keys(obj);
+  const result = {};
+  for (let i = 0; i < props.length; i++) {
+    // pass all properties in obj into cb
+    result[props[i]] = cb(obj[props[i]]);
+  }
+  return result;
 };
 
 const pairs = (obj) => {
   // Convert an object into a list of [key, value] pairs.
   // http://underscorejs.org/#pairs
+  // output: list of key : value pairs in obj
+  return Object.entries(obj);
 };
 
 /* STRETCH PROBLEMS */
@@ -29,12 +42,39 @@ 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
+  // method #1: use a loop
+  // let result = {}; // holds the inverted key value pairs
+  // let keys = Object.keys(obj);
+  // let vals = Object.values(obj);
+  // // iterate over obj's keys
+  // for (let key of keys) {
+  //   // set props in result to be values of obj
+  //   // values of result will be the properties of obj
+  //   result[obj[key]] = key;
+  // }
+  // return result;
+  // method #2: use array.reduce()
+  return Object.keys(obj).reduce((a, b) => {
+    // initial value of a is {}
+    // set each of obj's keys to a property in a
+    a[obj[b]] = b;
+    // a accumulates inverted key:value pairs
+    return a;
+  }, {});
+  // output: an object with obj's keys as values and obj's values as properties
 };
 
 const defaults = (obj, defaultProps) => {
   // Fill in undefined properties that match properties on the `defaultProps` parameter object.
   // Return `obj`.
   // http://underscorejs.org/#defaults
+  const props = Object.keys(defaultProps);
+  props.forEach((prop) => {
+    if (obj[prop] === undefined) {
+      obj[prop] = defaultProps[prop];
+    }
+  });
+  return obj;
 };
 
 /* eslint-enable no-unused-vars */