Aryan Srivastava

Top JavaScript String Interview Questions: DSA and Coding Challenges

Prepare for JavaScript interviews with these essential string-related coding questions. Learn key concepts, explore data structure and algorithm (DSA) challenges, and master string manipulation techniques for technical interviews.

Key Points about Strings in JavaScript:

  1. String Definition: In JavaScript, a string is a sequence of characters enclosed within single (' '), double (" "), or backticks (` `).
  2. String Immutability: Strings in JavaScript are immutable, meaning once created, their content cannot be changed directly.
  3. String Methods: JavaScript provides many built-in methods for string manipulation, such as:
    • charAt(), concat(), includes()
    • charAt(), concat(), includes()
    • slice(), substring(), substr()
    • split(), replace(), replaceAll()
    • trim(), toLowerCase(), toUpperCase()
  4. Template Literals: Introduced in ES6, template literals allow embedding expressions within strings using ${expression} and support multi-line strings.
  5. Escape Sequences: Special characters can be used in strings with escape sequences (e.g., \n for a new line, \' for single quotes).
  6. String Coercion: JavaScript automatically converts non-string data types to strings when necessary (e.g., during concatenation).
  7. Unicode and UTF-16: JavaScript strings are based on UTF-16 encoding, allowing support for Unicode characters.
  8. String Length: You can determine the length of a string using .length.

Important Interview Questions:

Q1: How can you find the length of a string in JavaScript?

Answer: Use the .length property.

Q2: How can you reverse a string in JavaScript?

Answer: You can convert the string to an array, reverse it, and join it back into a string.

Q3: What is the difference between slice(), substring(), and substr()?

Answer:

  • slice(start, end): Extracts a part of the string from start to end (not including end). It supports negative indexes.
  • substring(start, end): Similar to slice(), but does not support negative indexes.
  • substr(start, length): Extracts a substring starting from start and continuing for length characters.

Q4: How do you check if a string contains a substring in JavaScript?

Answer: Use the includes() method or indexOf().

Q5: How can you convert a string to uppercase and lowercase in JavaScript?

Answer: Use the toUpperCase() and toLowerCase() methods.

Q6: How would you replace all occurrences of a substring in a string?

Answer: Use the replaceAll() method (ES2021), or with a regular expression and the replace() method.

Q7: How do you extract a portion of a string without modifying the original string?

Answer: You can use slice(), substring(), or substr() to extract a portion without changing the original string.

Q8: What is template literal in JavaScript and how do you use it?

Answer: Template literals are a new way to create strings in ES6 using backticks (`). They support multi-line strings and variable interpolation.

Q9: What is template literal in JavaScript and how do you use it?

Answer:

In JavaScript, there are two ways to create strings: string literals and string objects.

A string literal is a simple and most common way to create a string using single quotes (‘ ‘), double quotes (” “), or backticks (` `).

A string object is created using the new String() constructor, which wraps a primitive string into an object.

Q10: How can you split a string into an array in JavaScript?

Answer: Use the split() method, specifying the delimiter.

Q11: What are escape sequences in JavaScript strings?

Answer: Escape sequences allow you to insert special characters like \n for new lines, \t for tabs, etc.

Q11: What are escape sequences in JavaScript strings?

Answer: Escape sequences allow you to insert special characters like \n for new lines, \t for tabs, etc.

DSA-Based Interview Questions on Strings:

Q1: How would you check if two strings are anagrams?

Answer:

Two strings are anagrams if they contain the same characters with the same frequency. One way to do this is by sorting both strings and comparing them.

Q2: How do you check if a string is a palindrome?

Answer:

A string is a palindrome if it reads the same backward and forward. You can reverse the string and check if it’s equal to the original string.

Q3: Find the first non-repeating character in a string.

Answer:

A string is a palindrome if it reads the same backward and forward. You can reverse the string and check if it’s equal to the original string.

Q4: How would you check if a string contains all unique characters?

Answer:

You can use a set to track the characters and check for duplicates.

Q5: How do you remove duplicate characters from a string?

Answer:

You can use a set to store unique characters and then join them back into a string.

Q6: How would you count and return the frequency of each character in a string?

Answer:

You can use a hash map (or object) to store the frequency of each character.

Conclusion

In today’s fast-paced tech environment, preparing for JavaScript interviews is critical, especially when it comes to string manipulation and data structure and algorithm (DSA) challenges. By mastering key string-related concepts like reversing strings, checking palindromes, anagrams, and more complex algorithms like the longest common prefix, you’ll strengthen your problem-solving skills and boost your confidence during coding interviews.