String Reversal Approaches in DSA Javascript - Build from Scratch

String Reversal Approaches

📖 Scenario: Imagine you are building a simple tool that helps users reverse words they type. This is useful in games, puzzles, or just for fun.

🎯 Goal: You will create a program that takes a fixed word, then reverses it using a step-by-step approach. You will learn how to work with strings and loops in JavaScript.

📋 What You'll Learn

Create a string variable with a specific word

Create a variable to hold the reversed string

Use a for loop to reverse the string character by character

Print the reversed string

💡 Why This Matters

🌍 Real World

Reversing strings is useful in puzzles, coding challenges, and some text processing tasks.

💼 Career

Understanding string manipulation and loops is fundamental for many programming jobs, including web development and software engineering.

1

Create the original string

Create a string variable called original and set it to the exact value "hello".

DSA Javascript

// Your code here
// Create the string variable original with value "hello"

Hint

Use const to create a string variable named original and assign it the word "hello".

2

Create a variable to hold the reversed string

Create a string variable called reversed and set it to an empty string "".

DSA Javascript

const original = "hello";
// Your code here
// Create the string variable reversed and set it to an empty string

Hint

Use let to create a variable named reversed and assign it an empty string.

3

Reverse the string using a for loop

Use a for loop with a variable i starting from original.length - 1 down to 0. Inside the loop, add original[i] to reversed.

DSA Javascript

const original = "hello";
let reversed = "";
// Your code here
// Use a for loop to reverse the string

Hint

Start the loop from the last character index and move backwards to the first character, adding each character to reversed.

4

Print the reversed string

Write a console.log statement to print the value of reversed.

DSA Javascript

const original = "hello";
let reversed = "";
for (let i = original.length - 1; i >= 0; i--) {
    reversed += original[i];
}
// Your code here
// Print the reversed string

Hint

Use console.log(reversed) to show the reversed word in the console.

Practice

1. What does the JavaScript method split('') do when applied to a string?

easy

A. It reverses the string characters.

B. It removes all spaces from the string.

C. It joins array elements into a string.

D. It converts the string into an array of individual characters.

Solution

1. Step 1: Understand the split method

   The split('') method splits a string into an array by each character because the separator is an empty string.

2. Step 2: Effect on string

   For example, 'hello'.split('') becomes ['h', 'e', 'l', 'l', 'o'].

3. Final Answer:

   It converts the string into an array of individual characters. -> Option D

4. Quick Check:

   split('') = array of chars [OK]

Hint: split('') breaks string into chars array [OK]

Common Mistakes:

• Thinking split('') reverses the string
• Confusing split('') with join()
• Assuming split('') removes spaces

2. Which of the following is the correct syntax to reverse a string str in JavaScript using built-in methods?

easy

A. str.reverse().join('')

B. str.split('').reverse().join('')

C. reverse(str).split('').join('')

D. str.join('').reverse()

Solution

1. Step 1: Understand string and array methods

   Strings do not have a reverse() method, but arrays do. So first convert string to array using split('').

2. Step 2: Reverse array and join back

   Use reverse() on the array, then join('') to convert back to string.

3. Final Answer:

   str.split('').reverse().join('') -> Option B

4. Quick Check:

   split + reverse + join = reversed string [OK]

Hint: Split string, reverse array, join back [OK]

Common Mistakes:

• Trying to call reverse() directly on string
• Using join() before reverse()
• Using incorrect method order

3. What is the output of the following code?

const str = 'abc';
const reversed = str.split('').reverse().join('');
console.log(reversed);

medium

A. Error: reverse is not a function

B. 'abc'

C. 'cba'

D. ['c', 'b', 'a']

Solution

1. Step 1: Split string into array

   'abc'.split('') becomes ['a', 'b', 'c'].

2. Step 2: Reverse array and join

   ['a', 'b', 'c'].reverse() becomes ['c', 'b', 'a'], then .join('') makes it 'cba'.

3. Final Answer:

   'cba' -> Option C

4. Quick Check:

   split + reverse + join = 'cba' [OK]

Hint: Split, reverse, join outputs reversed string [OK]

Common Mistakes:

• Expecting original string output
• Expecting array output instead of string
• Confusing method order causing errors

4. Identify the error in this string reversal code:

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

medium

A. Strings do not have reverse() method.

B. join() cannot be used on strings.

C. Function missing return statement.

D. split('') is missing before reverse().

Solution

1. Step 1: Check string methods

   Strings do not have reverse(), so calling s.reverse() causes error.

2. Step 2: Fix by splitting string

   We must convert string to array first using s.split('') before reversing.

3. Final Answer:

   Strings do not have reverse() method. -> Option A

4. Quick Check:

   No reverse() method on strings [OK]

Hint: Strings do not have reverse() method [OK]

Common Mistakes:

• Trying to reverse string directly
• Ignoring need to split string
• Misunderstanding join() usage

5. Given the function below, what will reverseString('hello world') return?

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

hard

A. 'dlrow olleh'

B. 'hello world'

C. 'helloworld'

D. Error: Cannot read property 'length' of undefined

Solution

1. Step 1: Loop from end to start

   The for loop starts at last character index and moves backward to 0, appending each character to reversed.

2. Step 2: Build reversed string

   Characters are added in reverse order, so 'hello world' becomes 'dlrow olleh'.

3. Final Answer:

   'dlrow olleh' -> Option A

4. Quick Check:

   Loop backward appends chars reversed [OK]

Hint: Loop backward to build reversed string [OK]

Common Mistakes:

• Looping forward instead of backward
• Not appending characters correctly
• Confusing string concatenation