JavaScript Coding Interview Questions

JavaScript is one of the most widely used programming languages in the world, making it a common focus in technical interviews for web development roles. In this article, we dive into common JavaScript coding interview questions with practical tips and solutions to help you succeed.

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Reverse a String: A Classic Coding Challenge

Problem: Write a function to reverse a given string.

Example:

Input:

"hello"

Output:

"olleh"

Solution:

Using a for loop:

function reverseString(str) {
    let reversed = "";
    for (let i = str.length - 1; i >= 0; i--) {
        reversed += str[i];
    }
    return reversed;
}

// Example usage
const reversedString = reverseString("hello");
console.log(reversedString); // Output: "olleh"

Using built-in methods:

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

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

Tip: This question is commonly asked to test your understanding of string and array manipulation. Highlight your ability to solve it using different approaches.

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Find the First Non-Repeating Character: Object and Loop Mastery

Problem: Write a function that finds the first non-repeating character in a string.

Example:

Input:

"swiss"

Output:

"w"

Solution:

function firstNonRepeatingChar(str) {
  const charCount = {};

  // Count occurrences of each character
  for (let char of str) {
    charCount[char] = (charCount[char] || 0) + 1;
  }

  // Find the first character with a count of 1
  for (let char of str) {
    if (charCount[char] === 1) {
      return char;
    }
  }

  return null;
}

console.log(firstNonRepeatingChar("test")); // Output: "e"

Tip: Practice this question to demonstrate your ability to use objects for counting and efficiently solve problems.

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Check for Anagrams: String Manipulation Made Simple

Problem: Write a function to check if two strings are anagrams of each other.

Example:

Input:

"listen", "silent"

Output:

true

Solution:

function areAnagrams(str1, str2) {
  if (str1.length !== str2.length) return false;

  const sortedStr1 = Array.from(str1).sort().join('');
  const sortedStr2 = Array.from(str2).sort().join('');

  return sortedStr1 === sortedStr2;
}

console.log(areAnagrams("eat", "tea")); // Output: true

Tip: Discuss the time complexity of sorting in your solution to showcase your knowledge of algorithmic efficiency.

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Remove Duplicates from an Array: Simplify Your Data

Problem: Write a function to remove duplicate elements from an array.

Example:

Input:

[1, 2, 2, 3, 4, 4, 5]

Output:

[1, 2, 3, 4, 5]

Solution:

Using a for loop:

function removeDuplicates(arr) {
  const result = [];
  for (let i = 0; i < arr.length; i++) {
    if (!result.includes(arr[i])) {
      result.push(arr[i]);
    }
  }
  return result;
}

// Example usage
const input = [1, 2, 2, 2, 3, 4, 4, 5, 5];
console.log(removeDuplicates(input)); // Output: [1, 2, 3, 4, 5]

Using a Set:

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

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

Tip: Use the Set approach to highlight your knowledge of ES6 features and their advantages in coding challenges.

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Final Tips for JavaScript Coding Interviews

1. Understand the Problem: Carefully read and clarify the requirements before starting.

2. Write Clean Code: Use meaningful variable names and add comments where necessary to enhance readability.

3. Optimize Solutions: Discuss the time and space complexity of your solution to showcase your understanding of algorithms.

4. Test Your Code: Always include edge cases to ensure your code works under various conditions.

Keep practicing, and good luck!