diff --git a/01_helloWorld/solution/helloWorld-solution.js b/01_helloWorld/solution/helloWorld-solution.js
new file mode 100644
index 0000000..002f305
--- /dev/null
+++ b/01_helloWorld/solution/helloWorld-solution.js
@@ -0,0 +1,5 @@
+const helloWorld = function () {
+    return 'Hello, World!';
+};
+
+module.exports = helloWorld;
diff --git a/01_helloWorld/solution/helloWorld-solution.spec.js b/01_helloWorld/solution/helloWorld-solution.spec.js
new file mode 100644
index 0000000..364645d
--- /dev/null
+++ b/01_helloWorld/solution/helloWorld-solution.spec.js
@@ -0,0 +1,7 @@
+const helloWorld = require('./helloWorld-solution');
+
+describe('Hello World', function () {
+    test('says "Hello, World!"', function () {
+        expect(helloWorld()).toEqual('Hello, World!');
+    });
+});
diff --git a/02_repeatString/solution/repeatString-solution.js b/02_repeatString/solution/repeatString-solution.js
new file mode 100644
index 0000000..e8ea93e
--- /dev/null
+++ b/02_repeatString/solution/repeatString-solution.js
@@ -0,0 +1,10 @@
+const repeatString = function (word, times) {
+    if (times < 0) return 'ERROR';
+    let string = '';
+    for (let i = 0; i < times; i++) {
+        string += word;
+    }
+    return string;
+};
+
+module.exports = repeatString;
diff --git a/02_repeatString/solution/repeatString-solution.spec.js b/02_repeatString/solution/repeatString-solution.spec.js
new file mode 100644
index 0000000..299874b
--- /dev/null
+++ b/02_repeatString/solution/repeatString-solution.spec.js
@@ -0,0 +1,41 @@
+const repeatString = require('./repeatString-solution');
+
+describe('repeatString', () => {
+    test('repeats the string', () => {
+        expect(repeatString('hey', 3)).toEqual('heyheyhey');
+    });
+    test.skip('repeats the string many times', () => {
+        expect(repeatString('hey', 10)).toEqual(
+            'heyheyheyheyheyheyheyheyheyhey'
+        );
+    });
+    test.skip('repeats the string 1 times', () => {
+        expect(repeatString('hey', 1)).toEqual('hey');
+    });
+    test.skip('repeats the string 0 times', () => {
+        expect(repeatString('hey', 0)).toEqual('');
+    });
+    test.skip('returns ERROR with negative numbers', () => {
+        expect(repeatString('hey', -1)).toEqual('ERROR');
+    });
+    test.skip('repeats the string a random amount of times', function () {
+        /*The number is generated by using Math.random to get a value from between
+    0 to 1, when this is multiplied by 1000 and rounded down with Math.floor it 
+    equals a number between 0 to 999 (this number will change everytime you run
+    the test).*/
+
+        // DO NOT use Math.floor(Math.random() * 1000) in your code,
+        // this test generates a random number, then passes it into your code with a function parameter.
+        // If this doesn't make sense, you should go read about functions here: https://www.theodinproject.com/paths/foundations/courses/foundations/lessons/fundamentals-part-3
+        const number = Math.floor(Math.random() * 1000);
+        /*The .match(/((hey))/g).length is a regex that will count the number of heys
+    in the result, which if your function works correctly will equal the number that
+    was randomaly generated. */
+        expect(repeatString('hey', number).match(/((hey))/g).length).toEqual(
+            number
+        );
+    });
+    test.skip('works with blank strings', () => {
+        expect(repeatString('', 10)).toEqual('');
+    });
+});
diff --git a/03_reverseString/solution/reverseString-solution.js b/03_reverseString/solution/reverseString-solution.js
new file mode 100644
index 0000000..7aee226
--- /dev/null
+++ b/03_reverseString/solution/reverseString-solution.js
@@ -0,0 +1,5 @@
+const reverseString = function (string) {
+    return string.split('').reverse().join('');
+};
+
+module.exports = reverseString;
diff --git a/03_reverseString/solution/reverseString-solution.spec.js b/03_reverseString/solution/reverseString-solution.spec.js
new file mode 100644
index 0000000..94b2624
--- /dev/null
+++ b/03_reverseString/solution/reverseString-solution.spec.js
@@ -0,0 +1,18 @@
+const reverseString = require('./reverseString-solution');
+
+describe('reverseString', () => {
+    test('reverses single word', () => {
+        expect(reverseString('hello')).toEqual('olleh');
+    });
+
+    test.skip('reverses multiple words', () => {
+        expect(reverseString('hello there')).toEqual('ereht olleh');
+    });
+
+    test.skip('works with numbers and punctuation', () => {
+        expect(reverseString('123! abc!')).toEqual('!cba !321');
+    });
+    test.skip('works with blank strings', () => {
+        expect(reverseString('')).toEqual('');
+    });
+});
diff --git a/04_removeFromArray/solution/removeFromArray-solution.js b/04_removeFromArray/solution/removeFromArray-solution.js
new file mode 100644
index 0000000..7399ed8
--- /dev/null
+++ b/04_removeFromArray/solution/removeFromArray-solution.js
@@ -0,0 +1,31 @@
+// we have 2 solutions here, an easier one and a more advanced one.
+// The easiest way to get an array of all of the arguments that are passed to a function
+// is using the rest operator. If this is unfamiliar to you look it up!
+const removeFromArray = function (...args) {
+    // the very first item in our list of arguments is the array, we pull it out with args[0]
+    const array = args[0];
+    // create a new empty array
+    const newArray = [];
+    // use forEach to go through the array
+    array.forEach((item) => {
+        // push every element into the new array
+        // UNLESS it is included in the function arguments
+        // so we create a new array with every item, except those that should be removed
+        if (!args.includes(item)) {
+            newArray.push(item);
+        }
+    });
+    // and return that array
+    return newArray;
+};
+
+// A simpler, but more advanced way to do it is to use the 'filter' function,
+// which basically does what we did with the forEach above.
+
+// var removeFromArray = function(...args) {
+//   const array = args[0]
+//   return array.filter(val => !args.includes(val))
+// }
+//
+
+module.exports = removeFromArray;
diff --git a/04_removeFromArray/solution/removeFromArray-solution.spec.js b/04_removeFromArray/solution/removeFromArray-solution.spec.js
new file mode 100644
index 0000000..bc1eb1a
--- /dev/null
+++ b/04_removeFromArray/solution/removeFromArray-solution.spec.js
@@ -0,0 +1,28 @@
+const removeFromArray = require('./removeFromArray-solution');
+
+describe('removeFromArray', () => {
+    test('removes a single value', () => {
+        expect(removeFromArray([1, 2, 3, 4], 3)).toEqual([1, 2, 4]);
+    });
+    test.skip('removes multiple values', () => {
+        expect(removeFromArray([1, 2, 3, 4], 3, 2)).toEqual([1, 4]);
+    });
+    test.skip('ignores non present values', () => {
+        expect(removeFromArray([1, 2, 3, 4], 7, 'tacos')).toEqual([1, 2, 3, 4]);
+    });
+    test.skip('ignores non present values, but still works', () => {
+        expect(removeFromArray([1, 2, 3, 4], 7, 2)).toEqual([1, 3, 4]);
+    });
+    test.skip('can remove all values', () => {
+        expect(removeFromArray([1, 2, 3, 4], 1, 2, 3, 4)).toEqual([]);
+    });
+    test.skip('works with strings', () => {
+        expect(removeFromArray(['hey', 2, 3, 'ho'], 'hey', 3)).toEqual([
+            2,
+            'ho',
+        ]);
+    });
+    test.skip('only removes same type', () => {
+        expect(removeFromArray([1, 2, 3], '1', 3)).toEqual([1, 2]);
+    });
+});
diff --git a/05_sumAll/solution/sumAll-solution.js b/05_sumAll/solution/sumAll-solution.js
new file mode 100644
index 0000000..9d95b64
--- /dev/null
+++ b/05_sumAll/solution/sumAll-solution.js
@@ -0,0 +1,16 @@
+const sumAll = function (min, max) {
+    if (!Number.isInteger(min) || !Number.isInteger(max)) return 'ERROR';
+    if (min < 0 || max < 0) return 'ERROR';
+    if (min > max) {
+        const temp = min;
+        min = max;
+        max = temp;
+    }
+    let sum = 0;
+    for (let i = min; i < max + 1; i++) {
+        sum += i;
+    }
+    return sum;
+};
+
+module.exports = sumAll;
diff --git a/05_sumAll/solution/sumAll-solution.spec.js b/05_sumAll/solution/sumAll-solution.spec.js
new file mode 100644
index 0000000..ba30f62
--- /dev/null
+++ b/05_sumAll/solution/sumAll-solution.spec.js
@@ -0,0 +1,22 @@
+const sumAll = require('./sumAll-solution');
+
+describe('sumAll', () => {
+    test('sums numbers within the range', () => {
+        expect(sumAll(1, 4)).toEqual(10);
+    });
+    test.skip('works with large numbers', () => {
+        expect(sumAll(1, 4000)).toEqual(8002000);
+    });
+    test.skip('works with larger number first', () => {
+        expect(sumAll(123, 1)).toEqual(7626);
+    });
+    test.skip('returns ERROR with negative numbers', () => {
+        expect(sumAll(-10, 4)).toEqual('ERROR');
+    });
+    test.skip('returns ERROR with non-number parameters', () => {
+        expect(sumAll(10, '90')).toEqual('ERROR');
+    });
+    test.skip('returns ERROR with non-number parameters', () => {
+        expect(sumAll(10, [90, 1])).toEqual('ERROR');
+    });
+});
diff --git a/06_leapYears/solution/leapYears-solution.js b/06_leapYears/solution/leapYears-solution.js
new file mode 100644
index 0000000..31898b7
--- /dev/null
+++ b/06_leapYears/solution/leapYears-solution.js
@@ -0,0 +1,5 @@
+const leapYears = function (year) {
+    return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
+};
+
+module.exports = leapYears;
diff --git a/06_leapYears/solution/leapYears-solution.spec.js b/06_leapYears/solution/leapYears-solution.spec.js
new file mode 100644
index 0000000..bcc422c
--- /dev/null
+++ b/06_leapYears/solution/leapYears-solution.spec.js
@@ -0,0 +1,22 @@
+const leapYears = require('./leapYears-solution');
+
+describe('leapYears', () => {
+    test('works with non century years', () => {
+        expect(leapYears(1996)).toBe(true);
+    });
+    test.skip('works with non century years', () => {
+        expect(leapYears(1997)).toBe(false);
+    });
+    test.skip('works with ridiculously futuristic non century years', () => {
+        expect(leapYears(34992)).toBe(true);
+    });
+    test.skip('works with century years', () => {
+        expect(leapYears(1900)).toBe(false);
+    });
+    test.skip('works with century years', () => {
+        expect(leapYears(1600)).toBe(true);
+    });
+    test.skip('works with century years', () => {
+        expect(leapYears(700)).toBe(false);
+    });
+});
diff --git a/07_tempConversion/solution/tempConversion-solution.js b/07_tempConversion/solution/tempConversion-solution.js
new file mode 100644
index 0000000..a5fad55
--- /dev/null
+++ b/07_tempConversion/solution/tempConversion-solution.js
@@ -0,0 +1,12 @@
+const ftoc = function (f) {
+    return Math.round((f - 32) * (5 / 9) * 10) / 10;
+};
+
+const ctof = function (c) {
+    return Math.round(((c * 9) / 5 + 32) * 10) / 10;
+};
+
+module.exports = {
+    ftoc,
+    ctof,
+};
diff --git a/07_tempConversion/solution/tempConversion-solution.spec.js b/07_tempConversion/solution/tempConversion-solution.spec.js
new file mode 100644
index 0000000..001351d
--- /dev/null
+++ b/07_tempConversion/solution/tempConversion-solution.spec.js
@@ -0,0 +1,25 @@
+const { ftoc, ctof } = require('./tempConversion-solution');
+
+describe('ftoc', () => {
+    test('works', () => {
+        expect(ftoc(32)).toEqual(0);
+    });
+    test.skip('rounds to 1 decimal', () => {
+        expect(ftoc(100)).toEqual(37.8);
+    });
+    test.skip('works with negatives', () => {
+        expect(ftoc(-100)).toEqual(-73.3);
+    });
+});
+
+describe('ctof', () => {
+    test.skip('works', () => {
+        expect(ctof(0)).toEqual(32);
+    });
+    test.skip('rounds to 1 decimal', () => {
+        expect(ctof(73.2)).toEqual(163.8);
+    });
+    test.skip('works with negatives', () => {
+        expect(ctof(-10)).toEqual(14);
+    });
+});
diff --git a/08_calculator/solution/calculator-solution.js b/08_calculator/solution/calculator-solution.js
new file mode 100644
index 0000000..ea9874a
--- /dev/null
+++ b/08_calculator/solution/calculator-solution.js
@@ -0,0 +1,48 @@
+const add = function (a, b) {
+    return a + b;
+};
+
+const subtract = function (a, b) {
+    return a - b;
+};
+
+const sum = function (array) {
+    return array.reduce((total, current) => total + current, 0);
+};
+
+const multiply = function (array) {
+    return array.length
+        ? array.reduce((accumulator, nextItem) => accumulator * nextItem)
+        : 0;
+};
+
+const power = function (a, b) {
+    return Math.pow(a, b);
+};
+
+const factorial = function (n) {
+    if (n === 0) return 1;
+    let product = 1;
+    for (let i = n; i > 0; i--) {
+        product *= i;
+    }
+    return product;
+};
+
+// This is another implementation of Factorial that uses recursion
+// THANKS to @ThirtyThreeB!
+const recursiveFactorial = function (n) {
+    if (n === 0) {
+        return 1;
+    }
+    return n * recursiveFactorial(n - 1);
+};
+
+module.exports = {
+    add,
+    subtract,
+    sum,
+    multiply,
+    power,
+    factorial,
+};
diff --git a/08_calculator/solution/calculator-solution.spec.js b/08_calculator/solution/calculator-solution.spec.js
new file mode 100644
index 0000000..3356e00
--- /dev/null
+++ b/08_calculator/solution/calculator-solution.spec.js
@@ -0,0 +1,77 @@
+const calculator = require('./calculator-solution');
+
+describe('add', () => {
+    test('adds 0 and 0', () => {
+        expect(calculator.add(0, 0)).toBe(0);
+    });
+
+    test.skip('adds 2 and 2', () => {
+        expect(calculator.add(2, 2)).toBe(4);
+    });
+
+    test.skip('adds positive numbers', () => {
+        expect(calculator.add(2, 6)).toBe(8);
+    });
+});
+
+describe('subtract', () => {
+    test.skip('subtracts numbers', () => {
+        expect(calculator.subtract(10, 4)).toBe(6);
+    });
+});
+
+describe('sum', () => {
+    test.skip('computes the sum of an empty array', () => {
+        expect(calculator.sum([])).toBe(0);
+    });
+
+    test.skip('computes the sum of an array of one number', () => {
+        expect(calculator.sum([7])).toBe(7);
+    });
+
+    test.skip('computes the sum of an array of two numbers', () => {
+        expect(calculator.sum([7, 11])).toBe(18);
+    });
+
+    test.skip('computes the sum of an array of many numbers', () => {
+        expect(calculator.sum([1, 3, 5, 7, 9])).toBe(25);
+    });
+});
+
+describe('multiply', () => {
+    test.skip('multiplies two numbers', () => {
+        expect(calculator.multiply([2, 4])).toBe(8);
+    });
+
+    test.skip('multiplies several numbers', () => {
+        expect(calculator.multiply([2, 4, 6, 8, 10, 12, 14])).toBe(645120);
+    });
+});
+
+describe('power', () => {
+    test.skip('raises one number to the power of another number', () => {
+        expect(calculator.power(4, 3)).toBe(64); // 4 to third power is 64
+    });
+});
+
+describe('factorial', () => {
+    test.skip('computes the factorial of 0', () => {
+        expect(calculator.factorial(0)).toBe(1); // 0! = 1
+    });
+
+    test.skip('computes the factorial of 1', () => {
+        expect(calculator.factorial(1)).toBe(1);
+    });
+
+    test.skip('computes the factorial of 2', () => {
+        expect(calculator.factorial(2)).toBe(2);
+    });
+
+    test.skip('computes the factorial of 5', () => {
+        expect(calculator.factorial(5)).toBe(120);
+    });
+
+    test.skip('computes the factorial of 10', () => {
+        expect(calculator.factorial(10)).toBe(3628800);
+    });
+});
diff --git a/09_palindromes/solution/palindromes-solution.js b/09_palindromes/solution/palindromes-solution.js
new file mode 100644
index 0000000..ffd5dbf
--- /dev/null
+++ b/09_palindromes/solution/palindromes-solution.js
@@ -0,0 +1,6 @@
+const palindromes = function (string) {
+    processedString = string.toLowerCase().replace(/[^a-z]/g, '');
+    return processedString.split('').reverse().join('') == processedString;
+};
+
+module.exports = palindromes;
diff --git a/09_palindromes/solution/palindromes-solution.spec.js b/09_palindromes/solution/palindromes-solution.spec.js
new file mode 100644
index 0000000..afcb47a
--- /dev/null
+++ b/09_palindromes/solution/palindromes-solution.spec.js
@@ -0,0 +1,24 @@
+const palindromes = require('./palindromes-solution');
+
+describe('palindromes', () => {
+    test('works with single words', () => {
+        expect(palindromes('racecar')).toBe(true);
+    });
+    test.skip('works with punctuation ', () => {
+        expect(palindromes('racecar!')).toBe(true);
+    });
+    test.skip('works with upper-case letters ', () => {
+        expect(palindromes('Racecar!')).toBe(true);
+    });
+    test.skip('works with multiple words', () => {
+        expect(palindromes('A car, a man, a maraca.')).toBe(true);
+    });
+    test.skip('works with multiple words', () => {
+        expect(
+            palindromes('Animal loots foliated detail of stool lamina.')
+        ).toBe(true);
+    });
+    test.skip("doesn't just always return true", () => {
+        expect(palindromes('ZZZZ car, a man, a maraca.')).toBe(false);
+    });
+});
diff --git a/10_fibonacci/solution/fibonacci-solution.js b/10_fibonacci/solution/fibonacci-solution.js
new file mode 100644
index 0000000..9f9a523
--- /dev/null
+++ b/10_fibonacci/solution/fibonacci-solution.js
@@ -0,0 +1,14 @@
+const fibonacci = function (count) {
+    if (count < 0) return 'OOPS';
+    if (count === 0) return 0;
+    let a = 0;
+    let b = 1;
+    for (let i = 1; i < count; i++) {
+        const temp = b;
+        b = a + b;
+        a = temp;
+    }
+    return b;
+};
+
+module.exports = fibonacci;
diff --git a/10_fibonacci/solution/fibonacci-solution.spec.js b/10_fibonacci/solution/fibonacci-solution.spec.js
new file mode 100644
index 0000000..997f30d
--- /dev/null
+++ b/10_fibonacci/solution/fibonacci-solution.spec.js
@@ -0,0 +1,31 @@
+const fibonacci = require('./fibonacci-solution');
+
+describe('fibonacci', () => {
+    test('4th fibonacci number is 3', () => {
+        expect(fibonacci(4)).toBe(3);
+    });
+    test.skip('6th fibonacci number is 8', () => {
+        expect(fibonacci(6)).toBe(8);
+    });
+    test.skip('10th fibonacci number is 55', () => {
+        expect(fibonacci(10)).toBe(55);
+    });
+    test.skip('15th fibonacci number is 610', () => {
+        expect(fibonacci(15)).toBe(610);
+    });
+    test.skip('25th fibonacci number is 75025', () => {
+        expect(fibonacci(25)).toBe(75025);
+    });
+    test.skip("doesn't accept negatives", () => {
+        expect(fibonacci(-25)).toBe('OOPS');
+    });
+    test.skip('DOES accept strings', () => {
+        expect(fibonacci('1')).toBe(1);
+    });
+    test.skip('DOES accept strings', () => {
+        expect(fibonacci('2')).toBe(1);
+    });
+    test.skip('DOES accept strings', () => {
+        expect(fibonacci('8')).toBe(21);
+    });
+});
diff --git a/11_getTheTitles/solution/getTheTitles-solution.js b/11_getTheTitles/solution/getTheTitles-solution.js
new file mode 100644
index 0000000..ebcf404
--- /dev/null
+++ b/11_getTheTitles/solution/getTheTitles-solution.js
@@ -0,0 +1,5 @@
+const getTheTitles = function (array) {
+    return array.map((book) => book.title);
+};
+
+module.exports = getTheTitles;
diff --git a/11_getTheTitles/solution/getTheTitles-solution.spec.js b/11_getTheTitles/solution/getTheTitles-solution.spec.js
new file mode 100644
index 0000000..e2dc20d
--- /dev/null
+++ b/11_getTheTitles/solution/getTheTitles-solution.spec.js
@@ -0,0 +1,18 @@
+const getTheTitles = require('./getTheTitles-solution');
+
+describe('getTheTitles', () => {
+    const books = [
+        {
+            title: 'Book',
+            author: 'Name',
+        },
+        {
+            title: 'Book2',
+            author: 'Name2',
+        },
+    ];
+
+    test('gets titles', () => {
+        expect(getTheTitles(books)).toEqual(['Book', 'Book2']);
+    });
+});
diff --git a/12_findTheOldest/solution/findTheOldest-solution.js b/12_findTheOldest/solution/findTheOldest-solution.js
new file mode 100644
index 0000000..d25a7ff
--- /dev/null
+++ b/12_findTheOldest/solution/findTheOldest-solution.js
@@ -0,0 +1,19 @@
+const findTheOldest = function (array) {
+    return array.reduce((oldest, currentPerson) => {
+        const oldestAge = getAge(oldest.yearOfBirth, oldest.yearOfDeath);
+        const currentAge = getAge(
+            currentPerson.yearOfBirth,
+            currentPerson.yearOfDeath
+        );
+        return oldestAge < currentAge ? currentPerson : oldest;
+    });
+};
+
+const getAge = function (birth, death) {
+    if (!death) {
+        death = new Date().getFullYear();
+    }
+    return death - birth;
+};
+
+module.exports = findTheOldest;
diff --git a/12_findTheOldest/solution/findTheOldest-solution.spec.js b/12_findTheOldest/solution/findTheOldest-solution.spec.js
new file mode 100644
index 0000000..2a33aff
--- /dev/null
+++ b/12_findTheOldest/solution/findTheOldest-solution.spec.js
@@ -0,0 +1,62 @@
+const findTheOldest = require('./findTheOldest-solution');
+
+describe('findTheOldest', () => {
+    test('finds the oldest person!', () => {
+        const people = [
+            {
+                name: 'Carly',
+                yearOfBirth: 1942,
+                yearOfDeath: 1970,
+            },
+            {
+                name: 'Ray',
+                yearOfBirth: 1962,
+                yearOfDeath: 2011,
+            },
+            {
+                name: 'Jane',
+                yearOfBirth: 1912,
+                yearOfDeath: 1941,
+            },
+        ];
+        expect(findTheOldest(people).name).toBe('Ray');
+    });
+    test.skip('finds the oldest person if someone is still living', () => {
+        const people = [
+            {
+                name: 'Carly',
+                yearOfBirth: 2018,
+            },
+            {
+                name: 'Ray',
+                yearOfBirth: 1962,
+                yearOfDeath: 2011,
+            },
+            {
+                name: 'Jane',
+                yearOfBirth: 1912,
+                yearOfDeath: 1941,
+            },
+        ];
+        expect(findTheOldest(people).name).toBe('Ray');
+    });
+    test.skip('finds the oldest person if the OLDEST is still living', () => {
+        const people = [
+            {
+                name: 'Carly',
+                yearOfBirth: 1066,
+            },
+            {
+                name: 'Ray',
+                yearOfBirth: 1962,
+                yearOfDeath: 2011,
+            },
+            {
+                name: 'Jane',
+                yearOfBirth: 1912,
+                yearOfDeath: 1941,
+            },
+        ];
+        expect(findTheOldest(people).name).toBe('Carly');
+    });
+});
diff --git a/13_caesar/solution/caesar-solution.js b/13_caesar/solution/caesar-solution.js
new file mode 100644
index 0000000..fed2bdf
--- /dev/null
+++ b/13_caesar/solution/caesar-solution.js
@@ -0,0 +1,26 @@
+const caesar = function (string, shift) {
+    return string
+        .split('')
+        .map((char) => shiftChar(char, shift))
+        .join('');
+};
+
+const codeSet = (code) => (code < 97 ? 65 : 97);
+
+// this function is just a fancy way of doing % so that it works with negative numbers
+// see this link for details:
+// https://stackoverflow.com/questions/4467539/javascript-modulo-gives-a-negative-result-for-negative-numbers
+const mod = (n, m) => ((n % m) + m) % m;
+
+const shiftChar = (char, shift) => {
+    const code = char.charCodeAt();
+
+    if ((code >= 65 && code <= 90) || (code >= 97 && code <= 122)) {
+        return String.fromCharCode(
+            mod(code + shift - codeSet(code), 26) + codeSet(code)
+        );
+    }
+    return char;
+};
+
+module.exports = caesar;
diff --git a/13_caesar/solution/caesar-solution.spec.js b/13_caesar/solution/caesar-solution.spec.js
new file mode 100644
index 0000000..68902ad
--- /dev/null
+++ b/13_caesar/solution/caesar-solution.spec.js
@@ -0,0 +1,23 @@
+const caesar = require('./caesar-solution');
+
+test('works with single letters', () => {
+    expect(caesar('A', 1)).toBe('B');
+});
+test.skip('works with words', () => {
+    expect(caesar('Aaa', 1)).toBe('Bbb');
+});
+test.skip('works with phrases', () => {
+    expect(caesar('Hello, World!', 5)).toBe('Mjqqt, Btwqi!');
+});
+test.skip('works with negative shift', () => {
+    expect(caesar('Mjqqt, Btwqi!', -5)).toBe('Hello, World!');
+});
+test.skip('wraps', () => {
+    expect(caesar('Z', 1)).toBe('A');
+});
+test.skip('works with large shift factors', () => {
+    expect(caesar('Hello, World!', 75)).toBe('Ebiil, Tloia!');
+});
+test.skip('works with large negative shift factors', () => {
+    expect(caesar('Hello, World!', -29)).toBe('Ebiil, Tloia!');
+});