Day 2: Reverse a String in JavaScript – 3 Methods for Coding Interviews

🚀 Day 2 – Reverse a String in JavaScript (Google/Amazon Favorite!)

Hello coders! 👋

Welcome back to Code With Jaffer – Day 2 of our JavaScript + DSA Interview Prep Series.

Today’s challenge is simple, but often asked in interviews at Google, Amazon, and TCS:

Reverse a string using different techniques.

Let’s solve it in 3 different ways, with clear code and explanation! 👇

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🧠 Problem Statement:

Q: Reverse a given string.

Input: "hello"

Output: "olleh"

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🔹 Method 1: Using JavaScript Built-in Functions

javascript
function reverseStringBuiltIn(str) {
  return str.split('').reverse().join('');
}
console.log(reverseStringBuiltIn("hello")); // Output: olleh

✅ Explanation:

• split('') converts the string to an array → ['h','e','l','l','o']

• reverse() reverses the array

• join('') joins it back into a string

🧠 Best for: Quick and clean solution.

⚡ Time Complexity: O(n)

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🔹 Method 2: Using a For Loop

javascript
function reverseStringLoop(str) {
  let reversed = '';
  for (let i = str.length - 1; i >= 0; i--) {
    reversed += str[i];
  }
  return reversed;
}
console.log(reverseStringLoop("hello")); // Output: olleh

✅ Explanation:

• Loop runs from end to start.

• Adds each character to the result string one by one.

🧠 Best for: Understanding logic flow manually.

⚡ Time Complexity: O(n)

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🔹 Method 3: Using Recursion

javascript
function reverseStringRecursion(str) {
  if (str === "") return "";
  return reverseStringRecursion(str.slice(1)) + str[0];
}
console.log(reverseStringRecursion("hello")); // Output: olleh

✅ Explanation:

• Base case: empty string

• Recursive case: reverse rest of the string + first character

🧠 Best for: Practicing recursion technique.

⚡ Time Complexity: O(n²) due to string slicing and concatenation

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🎯 Interview Tip:

• Explain each method clearly.

• Show you can think in multiple ways.

• Mention trade-offs in time/space complexity.

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