Challenges
Primitives

1. Swap two integers present in variables num1 and num2 without using temporary variable

  • The swapping of 2 variables is possible with simple Destructuring assignment using array
  • Traditional approach of swapping by using the given variables is also achievable
let num1 = 10, num2 = 20;
[num1, num2] = [num2, num1];
let num1 = 10, num2 = 20;
num1 = num1 + num2;
num2 = num1 - num2;
num1 = num1 - num2;

Notes

2nd solution can fail due to overflow of number range if the numbers are very big

2. Write a function which returns true if given value of number is an integer without using any inbuilt functions

// Example
isInt(4.0); // true
isInt(12.2); // false
isInt(0.3); // false
  • Modulo operator can be used to check if there is a remainder left when divided by 1
function isInt(value) {
  return value % 1 === 0;
}

3. Create a function which returns a random number in the given range of values both inclusive

  • Math.random function returns a floating-point, pseudo-random number between 0 (inclusive) and 1 (exclusive)
function randomNumberGeneratorInRange(rangeStart, rangeEnd) {
  return rangeStart + Math.round(Math.random() * (rangeEnd - rangeStart));
}
 
randomNumberGeneratorInRange(10, 50); // 12

Notes

Usage of Math.round depends on the logic used to accomplish the requirement

References

4. Write a program to reverse a string

  • String can be reversed by iterating it and storing it in reverse order
  • String can also be reversed by converting it to array, then joining it after reversing
const str = "JavaScript is awesome";
let reversedString = "";
for (let i = 0; i < str.length; i++) {
  reversedString = str.charAt(i) + reversedString;
}
 
reversedString; // "emosewa si tpircSavaJ"
const str = "JavaScript is awesome";
str.split("").reverse().join(""); // "emosewa si tpircSavaJ"

Notes

The string can be tested if it is palindrome, by comparing the actual string with the reversed string

References

5. Write a program to reverse a string by words. Also show the reverse of each words in place

  • The string can be reversed by words, by splitting the string with spaces and joining them back after reverse
  • If the the letters in each word have to be reversed, the string reversal procedure has to be followed after breaking the string with spaces
const str = "JavaScript is awesome";
str.split(" ").reverse().join(" "); // "awesome is JavaScript"
const str = "JavaScript is awesome";
str
  .split(" ")
  .map((val) => val.split("").reverse().join(""))
  .join(" "); // "tpircSavaJ si emosewa"

6. Write a program to reverse a given integer number

  • The remainder of the number can be fetched and the number can be divided by 10 to remove the digit in loop till number becomes 0
  • A simple approach to reverse a number could also be to convert it in to a string and then reverse it
let num = 3849;
 
let reversedNum = 0;
while (num !== 0) {
  reversedNum = reversedNum * 10 + (num % 10);
  num = Math.floor(num / 10);
}
 
reversedNum; // 9483
let num = 3849;
 
let numStr = String(num);
+numStr.split("").reverse().join(""); // 9483

7. Write a code to replace all the spaces of the string with underscores

  • The string can be split using the space character and can be joined back with underscore to replace all the spaces with strings
  • replaceAll is the inbuilt String function on prototype which can be used to replace a string with another string
str.split(" ").join("_");
str.replaceAll(" ", "_");

Notes

replace is also an inbuilt String function on prototype which can be used to replace the 1st occurrence of the string with another string

References

8. Write a function which can convert the time input given in 12 hours format to 24 hours format

// Example
convertTo24HrsFormat("12:10AM"); // 00:10
convertTo24HrsFormat("5:00AM"); // 05:00
convertTo24HrsFormat("12:33PM"); // 12:33
convertTo24HrsFormat("01:59PM"); // 13:59
convertTo24HrsFormat("11:8PM"); // 23:08
convertTo24HrsFormat("10:02PM"); // 22:02
  • The check for 'AM' and 'PM' can be verified using endsWith String method
  • An extra 0 would be needed if the hours have single digit
function convertTo24HrsFormat(timeText) {
  var timeTextLower = timeText.toLowerCase();
  let [hours, mins] = timeTextLower.split(":");
 
  // 12 o clock is the special case to be handled both for AM and PM
  if (timeTextLower.endsWith("am")) hours = hours == 12 ? "0" : hours;
  else if (timeTextLower.endsWith("pm"))
    hours = hours == 12 ? hours : String(+hours + 12);
 
  return hours.padStart(2, 0) + ":" + mins.slice(0, -2).padStart(2, 0);
}

Notes

Conversion of string to lowerCase helps in case insensitive comparision

References

9. Write a function which accepts a string argument and returns the count of characters between the first and last character 'X'

// Example
getTheGapX("XeroX"); // 4
getTheGapX("Xamarin"); // -1       (If there is only single character 'X')
getTheGapX("JavaScript"); // -1       (If there is no character 'X')
getTheGapX("F(X) !== G(X) !== F(X)"); // 18
  • indexOf and lastIndexOf are the methods on String which returns the position of the given string in the input string from start and end respectively
  • If the match is not found, these methods return -1
function getTheGapX(str) {
  if (!str.includes("X")) {
    return -1;
  }
 
  const firstIndex = str.indexOf("X");
  const lastIndex = str.lastIndexOf("X");
  return firstIndex === lastIndex ? -1 : lastIndex - firstIndex;
}

10. Write a function to truncate a string to a certain number of letters

// Example
truncateString("JavaScript", 7); // "Java..."
truncateString("JS is fun", 10); // "JS is fun"
truncateString("JS is funny", 10); // "JS is f..."
  • Text can be truncated by fetching the substring from start till the count of characters
  • substr methods of String can be used to fetch the part of the string
function truncateString(str, charCount) {
  if (str.length > charCount) {
    return str.substr(0, charCount - 3) + "...";
  } else {
    return str;
  }
}

11. Write a code to truncate a string to a certain number of words

  • The string can be broken in to words array and then slice method of array can be used to get the number of words which will then be joined back
const str = "JavaScript is simple but not easy to master";
const wordLimit = 3;
 
str.split(" ").slice(0, wordLimit).join(" "); // "JavaScript is simple"

12. Create a regular expression to validate if the given input is valid Indian mobile number or not

// Example
validateMobile("+919876543210"); // true
validateMobile("+91 9876543210"); // true
validateMobile("09876543210"); // true
validateMobile("9876543210"); // true
validateMobile("99876543210"); // false
  • Regular expression check has to have an optional +91 or 0 in the beginning, then an optional space and 10 digits
  • test method of regular expression can be used to validate if the mobile number pattern matches or not
function validateMobile(str) {
  const regexMobile = /^(\+91|0)?\s?\d{10}$/;
  return regexMobile.test(str);
}
function validateMobile(str) {
  const regexMobile = /^(\+91|0)?\s?\d{10}$/;
  return str.match(regexMobile) !== null;
}

Notes

String has method match which returns array of matches or null

13. Write a function which returns a list of elements which contains at least one character as digit

// Example
numInStr(['1a', 'a', '2b', 'b']));              // ['1a', '2b']
numInStr(['abc', 'abc10']));                    // ['abc10']
numInStr(['abc', 'ab10c', 'a10bc', 'bcd']));    // ['ab10c', 'a10bc']
numInStr(['this is a test', 'test1']));         // ['test1']
  • A test for digit after looping through the array would give the list of values having at least one digit string
function numInStr(mixArray) {
  return mixArray.filter((value) => {
    return /[0-9]/.test(value);
  });
}

14. Write a function which checks if a given search text is present either in the beginning of the first name or the second name

// Example
validateName("Nedson PETER", "pet"); // true
validateName("Peter Parker", "pet"); // true
validateName("Speter parker", "pet"); // false
validateName("John Doe Peter", "pet"); // false
  • The function can be designed to accept the name and the search text
  • Regular expression can be designed to validate if the name has search text the beginning of first or second name
function validateName(str, searchText) {
  const regex = new RegExp("^(\\w*\\s)?" + searchText + "\\w*?", "i");
  return regex.test(str);
}

Notes

Case insensitive match is happening for the search text in the string represented by the argument "i" for the regular expression

15. Write a function to chop a string into chunks of a given length and return it as array

// Example
stringChop("JavaScript"); // ["JavaScript"]
stringChop("JavaScript", 2); // ["Ja", "va", "Sc", "ri", "pt"]
stringChop("JavaScript", 3); // ["Jav", "aSc", "rip", "t"]
  • String can be chopped using slice method of String
  • Regular expression can also be used effectively to this operation
function stringChop(str, size = str.length) {
  const arr = [];
  let i = 0;
  while (i < str.length) {
    arr.push(str.slice(i, i + size));
    i = i + size;
  }
  return arr;
}
function stringChop(str, size = str.length) {
  return str.match(new RegExp(".{1," + size + "}", "g"));
}

References

16. Write a code to remove all the vowels from a given string

  • replace method on String accepts a string or regex as the argument
const str = "I love JavaScript";
str.replace(/[aeiou]/gi, ""); // _lv_JvScrpt

References

17. Create a function which returns random hex color code

  • The color code is popularly represented in hexadecimal format for RGB colors
  • The minimum value for the color is '#000000' and maximum is '#FFFFFF'
function getGetHEXColorCode() {
  const rValue = Math.round(0xff * Math.random())
    .toString(16)
    .padStart(2, "0");
  const gValue = Math.round(0xff * Math.random())
    .toString(16)
    .padStart(2, "0");
  const bValue = Math.round(0xff * Math.random())
    .toString(16)
    .padStart(2, "0");
  return "#" + rValue + gValue + bValue;
}

Notes

toString method on String takes optional parameter which converts converts to the specified base before converting to string

References

18. Write a function which accepts two valid dates and returns the difference between them as number of days

  • The difference between 2 dates in JavaScript will give the time difference in milliseconds
  • Time difference can be converted in to days by dividing the 24Hrs time in milliseconds
const DAY_IN_MILLISECONDS = 1000 * 60 * 60 * 24;
 
function getDaysBetweenDates(dateText1, dateText2) {
  const date1 = new Date(dateText1);
  const date2 = new Date(dateText2);
  const diffTime = Math.abs(date2 - date1);
  const diffDays = Math.ceil(diffTime / DAY_IN_MILLISECONDS);
  return diffDays;
}
 
getDaysBetweenDates("10/15/2020", "12/1/2020"); // 47

References

19. How can you detect NaN in JavaScript?

NaN is a special numeric value in JavaScript that indicates "Not-a-Number." You can use Number.isNaN() or isNaN() to check for NaN, though they behave differently.

 
console.log(Number.isNaN(NaN));           // true
console.log(Number.isNaN("hello"));       // false (doesn't coerce)
console.log(Number.isNaN(undefined));     // false
 
console.log(isNaN(NaN));                  // true
console.log(isNaN("hello"));              // true (coerces to NaN)
console.log(isNaN(undefined));            // true (coerces to NaN)

References

20. Show how to use Object.is for equality comparison between primitives

Object.is can be used to check strict equality between two values, especially in edge cases like NaN, 0 and -0, where === may behave differently.

 
console.log(Object.is(10, 10));               // true
console.log(Object.is("hello", "hello"));     // true
console.log(Object.is(NaN, NaN));             // true (different from ===)
console.log(Object.is(0, -0));                // false (different from ===)
console.log(Object.is(null, null));           // true
console.log(Object.is(undefined, undefined)); // true
console.log(Object.is(Symbol(), Symbol()));   // false (different symbols are unique)

References

VariablesFunctions