JavaScript Exercises

Solutions and explanation to JS exercises.

This is not a cheat sheet!

I made this compilation while solving JavaScript algorithms in FreeCodeCamp and Edabit. I thought this must be a helpful guide for people trying to get up and running in web development paradigm.

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Table Of Contents

• Find the Smallest number in an Array
• Sort Strings Alphabetically
• Factorialize a Number
• Indentify if a Number is Odd or Even
• Eliminating the Odds
• Numbers only
• Add all the numbers
• Min, Max, Length and Average
• Sort in Ascending Order
• Number to Roman Numerals (from FreeCodeCamp)
• Absolutely Sum
• Triangle Loop (from Eloquent JavaScript)
• Words Count
• Multiply by Length
• Ends with xxx
• Repeating Letters
• Index Location
• Do ... while loop
• License

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Find the smallest number in an array

Create a function that will display the smallest value in the array.

Example:

> console.log(findSmallest([30, 45, 60, 7]));
> 1

Reference:

• Math.min

Solution:

function findSmallest(arr) {
  return Math.min(...arr);
}

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Sort strings by Alphabetical Order

Function that will return your string in Alphabetical order

Example:

> console.log(AlphabeticalOrder('hello'));
> "ehllo"

Reference:

• Array.sort

• Array.split

• Array.join

Solution:

function AlphabeticalOrder(str) {
  return str
    .split("")
    .sort()
    .join("");
}

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Factorialize a number

In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. In simple terms, the Factorial of 7 is solved like this:

7 _ 6 _ 5 _ 4 _ 3 _ 2 _ 1 = 5,040

Example:

> console.log(factorializer(7));
> 5040

Reference:

• What is Factorial?

• Recursion

• If and Else statements

Solution:

function factorializer(int) {
  if (int <= 1) {
    return 1;
  } else {
    return int * factorializer(int - 1);
  }
}

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Identify if a number is Odd or Even?

A function that lets you know if a number is Even or Odd

Example:

> console.log(oddOrEven(7));
> "Odd"

Reference:

• Modulo

Solution:

function oddOrEven(int) {
  let ouput = int % 2;
  if (output == 0) {
    return "Even";
  } else {
    return "Odd";
  }
}

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Eliminate all odd numbers in an array.

Remove all Odd number(s) in an array and return a new array that contains Even numbers only

Example:

> console.log(evenOnly([1, 2, 3, 4, 5, 6]));
> [ 2, 4, 6 ]

Reference:

• Array.filter

• Modulo

Solution:

function evenOnly(arr) {
  let result = arr.filter(arr => arr % 2 == 0);
  return result;
}

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Return numbers only

Create a function that will accept an array, check the data type of each element. The function will delete string elements and will return a the new array

Example:

> console.log(numbersOnly(['text', 3, 7, 'github', 13, 'dev']));
> [ 3, 7, 13 ]

Reference:

• Array.filter

• typeof

Solution:

function numbersOnly(arr) {
  return arr.filter(arr => typeof arr == "number");
}

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Add up the numbers

Return the sum of a number going back to it's root. In other words, the function will work like this:

addUp(5);

// 5 + 4 + 3 + 2 + 1 + 0 = 15

Example:

> console.log(addUp(8));
> 36

Reference:

• Recursion

• 1 + 2 + 3 + 4 + ⋯

Solution:

function addUp(num) {
  if (num <= 1) {
    return num;
  } else {
    return num + addUp(num - 1);
  }
}

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Return the Min, Max, Length and Average of an Array

Create a function that will accept an array and do the following:

• Get the lowest element

• Get the highest element

• Get the length of array

• Get the Average of all element;

• Store these criteria in a new array

Example:

> console.log(minMaxLengthAverage([7, 13, 3, 77, 100]));
> [ 3, 100, 5, 40 ]

Reference:

• Math.min

• Math.max

• Array.reduce

• Array.length

Solution:

function minMaxLengthAverage(arr) {
  const min = Math.min(...arr);
  const max = Math.max(...arr);
  const len = arr.length;

  //Reducer for get Average function
  const ave = arr => arr.reduce((acc, curVal) => acc + curVal, 0) / len;
  const average = ave(arr);

  //Return output
  return [min, max, len, average];
}

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Sort Numbers in Ascending Order

Array.sort() sorts the strings alphabetically. What if we want to sort numbers from lowest to highest? Will it produce a correct output?

Example: This is what happen if we apply Array.sort() to numbers:

> arr = [45, 34, 23, 12, 7]
> console.log(arr.sort());
> [ 12, 23, 34, 45, 7 ]

Output is not correct right?, whereas we are expecting this to be the return value:

> console.log(sortNumsAscending([7, 13, 3, 77, 100]));
> [ 3, 5, 40, 100 ]

Reference:

• Sorting in JavaScript

• Array.sort()

Solution:

function sortNumsAscending(arr) {
  let sorter = (a, b) => {
    return a - b;
  };

  if (arr == []) {
    return [];
  } else if (arr == null) {
    return [];
  } else {
    return arr.sort(sorter);
  }
}

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Convert Numbers in Roman Numerals

Convert the given number to a Roman Numeral

Example:

> romanNumbers(1989);
> MCMLXXXIX

Reference:

• Roman Numerals

• Array.join()

• Array.indexOf()

• Array.splice()

Solution:

function romanNumbers(num) {
  let values = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1];
  let romanNumerals = [
    "M",
    "CM",
    "D",
    "CD",
    "C",
    "XC",
    "L",
    "XL",
    "X",
    "IX",
    "V",
    "IV",
    "I"
  ];

  let roman = "";

  for (i = 0; i < values.length; i++) {
    while (values[i] <= num) {
      roman += romanNumerals[i];
      num -= values[i];
    }
  }
  return roman;
}

console.log(romanNumbers(1989));

Absolutely Sum

Return the absolute sum of all the array elements

Example:

> getAbsSum([-1, -3, -5, -4, -10, 0]);
> 23

Reference:

• Array.prototype.reduce

• Math.abs

Solution:

function getAbsSum(arr) {
  const reducer = (acc, currVal) => {
    return acc + currVal;
  };

  return Math.abs(arr.reduce(reducer));
}

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Looping a Triangle

Form a triangle using hash tags

Example:

> #
> ##
> ###
> ####
> #####
> ######
> #######

Reference:

• Loop

Solution:

for (x = "#"; x.length <= 7; x += x) {
  console.log(x);
}

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Count the number of Words

Return how many words was given

Example:

> countWords('hello from kbpsystem!');
> 3

Reference:

• String.prototype.split

• Array.length

Solution:

function countWords(str) {
  return str.split(" ").length;
}

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Multiply by Length

Multiply all elements in an array by it's length

Example:

> MultiplyByLength([4,1,1]);
> [12, 3, 3]

Reference:

• for

• Array.length

• Array.prototype.push

• Array.prototype.map

Solution:

function MultiplyByLength(arr) {
  let len = arr.length;
  for (i = 0; i < len; i++) {
    arr[i] = arr[i] * len;
  }
  return arr;
}

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Ends With "xxx"

Create a function that will check if str1 ends with the characters in str2

Rules:

• Take two strings as argument

• Determine if second string matches ending of the first string

• Return boolean value

Example:

> console.log(checkEnding("samurai", "zi"));
> false

Reference:

• String.prototype.endsWith() method determines whether a string ends with the characters of a specified string, returning true or false as appropriate.

• Array.prototype.join method joins all elements of an array (or an array-like object) into a string and returns this string.

Solution:

function checkEnding(str1, str2) {
  return str1.endsWith(str2);
}

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Repeating Letters

Create a function that will repeat each string character two times

Example:

> console.log(doubleChar('exercise'));
> eexxeerrcciissee

Reference:

• Array.prototype.split The split() method splits a String object into an array of strings by separating the string into substrings, using a specified separator string to determine where to make each split.

• Array.prototype.map The map() method creates a new array with the results of calling a provided function on every element in the calling array.

• Array.prototype.join This method joins all elements of an array (or an array-like object) into a string and returns this string.

Solution:

function doubleChar(str) {
  let x = str.split("");
  return x.map(x => x.repeat(2)).join("");
}

Explanation: On the solution above, first we apply split method on the string argument and then store it in a variable called x. Next, we use the map function in order to performa duplication process on each element of the string, which was considered as array on this case because we just applied a split method on the string. Once duplication process is done, we call the join() method. Applying this method will convert the array back to being a string again but this time with a new duplicated values

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Find the correct Index location

Return the index location of an element from a given array. First argument is the array you'd like to search and the second one is the element (either string/number) to look for.

Example:

> console.log(findIndex(['github', 'gitlab', 'bitbucket', 'apollo'], 'gitlab'));
> 1

Reference:

• Array.Prototype.indexOf() The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present. Note that this method is not widely supported in all browsers so a Polyfill is needed.

Solution:

function findIndex(arr, element) {
  return arr.indexOf(element);
}

Explanation: findIndex function takes two arguments. First is the array to be monitored and then the last is the element on the array that needs to be located. JavaScript has a built in method called indexOf() and we used that in order to locate the index location of a certain element in an array. This method loops through the array locating the index value of an element

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Do run this function while

This exercise is courtesy of FreeCodeCamp

This exercise is an implementation of do while statement. Our goal here is to keep on running a function/statement, set a paramater and as soon as the result of the parameter evaluates to false, the function/statement execution will stop

Example:

var result = "";
var i = 0;

do {
  i = i + 1;
  result = result + i;
} while (i < 5);

console.log(result);
// expected result: "12345"

Reference:

• do while Definition from our friend in Mozilla:

  The do...while statement creates a loop that executes a specified statement until the test condition evaluates to false. The condition is evaluated after executing the statement, resulting in the specified statement executing at least once.

Solution:

// Setup
> var myArray = [];
> var i = 10;

> // Only change code below this line.
> do {
    myArray.push(i);
    i++;
    console.log(i)
} while (i < 11)

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MIT License | Copyright(c) 2018 Koleen Paunon