Javascript Coding Questions and Answers

Write a JavaScript function to reverse a string.

Use the following JavaScript code:

function reverseString(str) {
    return str.split('').reverse().join('');
}

console.log(reverseString("hello")); // Output: "olleh"

Write a JavaScript function to check if a number is prime.

Use the following JavaScript code:

function isPrime(num) {
    if (num <= 1) return false;
    for (let i = 2; i <= Math.sqrt(num); i++) {
        if (num % i === 0) return false;
    }
    return true;
}

console.log(isPrime(7)); // Output: true

Write a JavaScript function to find the factorial of a number.

Use the following JavaScript code:

function factorial(n) {
    if (n === 0 || n === 1) return 1;
    return n * factorial(n - 1);
}

console.log(factorial(5)); // Output: 120

Write a JavaScript function to flatten a nested array.

Use the following JavaScript code:

function flattenArray(arr) {
    return arr.flat(Infinity);
}

console.log(flattenArray([1, [2, [3, [4]]]])); // Output: [1, 2, 3, 4]

Write a JavaScript function to sort an array of objects by a specific property.

Use the following JavaScript code:

function sortByProperty(arr, prop) {
    return arr.sort((a, b) => (a[prop] > b[prop]) ? 1 : -1);
}

const people = [{ name: 'John', age: 30 }, { name: 'Jane', age: 25 }];
console.log(sortByProperty(people, 'age'));

Write a JavaScript function to find the longest word in a sentence.

Use the following JavaScript code:

function longestWord(sentence) {
    const words = sentence.split(' ');
    return words.reduce((longest, word) => word.length > longest.length ? word : longest, '');
}

console.log(longestWord("The quick brown fox jumped over the lazy dog")); // Output: "jumped"

Write a JavaScript function to remove duplicates from an array.

Use the following JavaScript code:

function removeDuplicates(arr) {
    return [...new Set(arr)];
}

console.log(removeDuplicates([1, 2, 2, 3, 4, 4, 5])); // Output: [1, 2, 3, 4, 5]

Write a JavaScript function to find the sum of all numbers in an array.

Use the following JavaScript code:

function sumArray(arr) {
    return arr.reduce((sum, num) => sum + num, 0);
}

console.log(sumArray([1, 2, 3, 4, 5])); // Output: 15

Write a JavaScript function to check if a string is a palindrome.

Use the following JavaScript code:

function isPalindrome(str) {
    const cleaned = str.replace(/[^a-zA-Z0-9]/g, '').toLowerCase();
    return cleaned === cleaned.split('').reverse().join('');
}

console.log(isPalindrome("A man, a plan, a canal, Panama")); // Output: true

Write a JavaScript function to merge two sorted arrays.

Use the following JavaScript code:

function mergeSortedArrays(arr1, arr2) {
    let i = 0, j = 0, result = [];
    while (i < arr1.length && j < arr2.length) {
        if (arr1[i] < arr2[j]) result.push(arr1[i++]);
        else result.push(arr2[j++]);
    }
    return result.concat(arr1.slice(i)).concat(arr2.slice(j));
}

console.log(mergeSortedArrays([1, 3, 5], [2, 4, 6])); // Output: [1, 2, 3, 4, 5, 6]

Write a JavaScript function to find the intersection of two arrays.

Use the following JavaScript code:

function intersectArrays(arr1, arr2) {
    return arr1.filter(value => arr2.includes(value));
}

console.log(intersectArrays([1, 2, 3, 4], [3, 4, 5, 6])); // Output: [3, 4]

Write a JavaScript function to generate a random integer between two values.

Use the following JavaScript code:

function getRandomInt(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(getRandomInt(1, 10)); // Output: a random integer between 1 and 10

Write a JavaScript function to count the occurrences of each character in a string.

Use the following JavaScript code:

function countChars(str) {
    return str.split('').reduce((count, char) => {
        count[char] = (count[char] || 0) + 1;
        return count;
    }, {});
}

console.log(countChars("hello")); // Output: { h: 1, e: 1, l: 2, o: 1 }

Write a JavaScript function to find the missing number in an array of 1 to n.

Use the following JavaScript code:

function findMissingNumber(arr, n) {
    const total = (n * (n + 1)) / 2;
    const sum = arr.reduce((a, b) => a + b, 0);
    return total - sum;
}

console.log(findMissingNumber([1, 2, 4, 5, 6], 6)); // Output: 3

Write a JavaScript function to debounce a function.

Use the following JavaScript code:

function debounce(func, delay) {
    let timeout;
    return function(...args) {
        clearTimeout(timeout);
        timeout = setTimeout(() => func.apply(this, args), delay);
    };
}

const debouncedFunc = debounce(() => console.log('Debounced!'), 300);
debouncedFunc(); // Debounced! (after 300ms)

Write a JavaScript function to check if two strings are anagrams.

Use the following JavaScript code:

function areAnagrams(str1, str2) {
    const normalize = str => str.replace(/[^a-zA-Z]/g, '').toLowerCase().split('').sort().join('');
    return normalize(str1) === normalize(str2);
}

console.log(areAnagrams("Listen", "Silent"));  // Output: true

Write a JavaScript function to find the longest substring without repeating characters.

Use the following JavaScript code:

function longestUniqueSubstring(str) {
    let start = 0, maxLength = 0, usedChars = {};
    
    for (let end = 0; end < str.length; end++) {
        if (usedChars[str[end]] !== undefined) {
            start = Math.max(start, usedChars[str[end]] + 1);
        }
        usedChars[str[end]] = end;
        maxLength = Math.max(maxLength, end - start + 1);
    }
    return maxLength;
}

console.log(longestUniqueSubstring("abcabcbb"));  // Output: 3

Write a JavaScript function to merge two sorted arrays into one sorted array.

Use the following JavaScript code:

function mergeSortedArrays(arr1, arr2) {
    let merged = [], i = 0, j = 0;

    while (i < arr1.length && j < arr2.length) {
        if (arr1[i] < arr2[j]) merged.push(arr1[i++]);
        else merged.push(arr2[j++]);
    }
    return merged.concat(arr1.slice(i)).concat(arr2.slice(j));
}

console.log(mergeSortedArrays([1, 3, 5], [2, 4, 6]));  // Output: [1, 2, 3, 4, 5, 6]

Write a JavaScript function to count the occurrences of each character in a string.

Use the following JavaScript code:

function countCharacterOccurrences(str) {
    const count = {};
    for (const char of str) {
        count[char] = (count[char] || 0) + 1;
    }
    return count;
}

console.log(countCharacterOccurrences("hello"));  // Output: { h: 1, e: 1, l: 2, o: 1 }

Write a JavaScript function to find the intersection of two arrays.

Use the following JavaScript code:

function arrayIntersection(arr1, arr2) {
    const set2 = new Set(arr2);
    return arr1.filter(item => set2.has(item));
}

console.log(arrayIntersection([1, 2, 3, 4], [3, 4, 5, 6]));  // Output: [3, 4]