Is there a way to reverse a string in Javascript without using any built-in functions?

Question

Is there a way to reverse a string in Javascript without using any built-in functions?

I am looking for a way to reverse a string without using built-in functions like split, reverse, and join. I came across this code snippet on Stack Overflow (), but I'm having trouble understanding what the code does on the fourth line. I need more clarification on that particular line. Below is the code along with some explanations:

 function reverseString(str) {
  reverseIt = [];
  for (i = 0; i < str.length; i++) {
    reverseIt = str[i] + reverseIt; // This is the first method that works
    // reverseIt = str[i] + [];    // I initially thought that variable "reverseIt" was equal to an empty array []
    // reverseIt = str[i] + '';    // I then tried assuming that reverseIt is an empty string "", but it did not give the expected result

    // var testing = [];             // I attempted to create an empty array variable again
    // reverseIt = str[i] + testing; // Added the above variable, but still didn't get the desired result
    /*
      My question is: why does the first method work? What exactly does the code on that line do?
    */
  }
  return reverseIt;
}
console.log(reverseString('Javascript'));

javascript arrays node.js for-loop

Answer 1

Answer №1

Essentially, the process outlined instructs to start from the first character and work towards the end, adding each new character before the existing string.

For instance, taking the name david, begin with an empty string, then prepend each letter consecutively at the front of the sequence. Beginning from nothing, add d, then include a in front to form ad, introduce v to create vad, continuing until the final result is divad

-> Your attempt in the code snippet:

reverseIt = str[i] + [];

differs from the original implementation since reverseIt starts as [] only initially! (Note that this [] equates to '' here given the nature of strings).

Initially, it is indeed [] (or '', same thing), but after one step, it becomes d! Then the subsequent str[i] is a which appends to

reverseIt</code now holding <code>d

, forming ad within reverseIt! This continues until the full reversal is achieved.

-> Your attempt with this alternative code:

var testing = [];
reverseIt = str[i] + testing;

is incorrect, as you are essentially resetting your reversed string at every iteration instead of concatenating the new string to what has been established previously. Each time, reverseIt switches from [] to d to a to v and so on, as it is constantly set equal to str[i] + testing. Since testing always remains as [], it effectively translates to: reverseIt = str[i], resulting in only retaining the last character of the input string by the end!

Answer 2

Essentially, the process outlined instructs to start from the first character and work towards the end, adding each new character before the existing string.

For instance, taking the name david, begin with an empty string, then prepend each letter consecutively at the front of the sequence. Beginning from nothing, add d, then include a in front to form ad, introduce v to create vad, continuing until the final result is divad

-> Your attempt in the code snippet:

reverseIt = str[i] + [];

differs from the original implementation since reverseIt starts as [] only initially! (Note that this [] equates to '' here given the nature of strings).

Initially, it is indeed [] (or '', same thing), but after one step, it becomes d! Then the subsequent str[i] is a which appends to

reverseIt</code now holding <code>d

, forming ad within reverseIt! This continues until the full reversal is achieved.

-> Your attempt with this alternative code:

var testing = [];
reverseIt = str[i] + testing;

is incorrect, as you are essentially resetting your reversed string at every iteration instead of concatenating the new string to what has been established previously. Each time, reverseIt switches from [] to d to a to v and so on, as it is constantly set equal to str[i] + testing. Since testing always remains as [], it effectively translates to: reverseIt = str[i], resulting in only retaining the last character of the input string by the end!

Answer 3

Answer №2

Take a moment to consider how the loop body execution's temporary result changes at different indexes in this line of code:

reverseIt = str[i] + reverseIt;

1. At the Start (i = 0)

reverseIt === str[0] + reverseIt === str[0] + []

Note that the plus operator will convert [] into a string, resulting in ''.

2. In-Between (0 < i < str.length):

reverseIt === str[i] + reversetIt === str[i] + (str[i - 1] + ... + str[0] + [])

3. At the End (i = n - 1):

reverseIt === str[n - 1] + reversetIt === str[n - 1] + (str[n - 2] + ... + str[0] + []) === str + []

If you've noticed the issue in the two problematic lines, there's an error in dropping the accumulated result. For each index

reverseIt === str[i] + []

and

reverseIt === str[i] + ''

This leads to ending up with a final string containing only the last character or an empty string.

Additionally, using Array.from and Array.reduce together can achieve the same outcome in a more concise manner:

const reverse = (s) => Array.from(s).reduce((result, c) => `${c}${result}`, '');

console.log(reverse('JavaScript'));

Answer 4

Take a moment to consider how the loop body execution's temporary result changes at different indexes in this line of code:

reverseIt = str[i] + reverseIt;

1. At the Start (i = 0)

reverseIt === str[0] + reverseIt === str[0] + []

Note that the plus operator will convert [] into a string, resulting in ''.

2. In-Between (0 < i < str.length):

reverseIt === str[i] + reversetIt === str[i] + (str[i - 1] + ... + str[0] + [])

3. At the End (i = n - 1):

reverseIt === str[n - 1] + reversetIt === str[n - 1] + (str[n - 2] + ... + str[0] + []) === str + []

If you've noticed the issue in the two problematic lines, there's an error in dropping the accumulated result. For each index

reverseIt === str[i] + []

and

reverseIt === str[i] + ''

This leads to ending up with a final string containing only the last character or an empty string.

Additionally, using Array.from and Array.reduce together can achieve the same outcome in a more concise manner:

const reverse = (s) => Array.from(s).reduce((result, c) => `${c}${result}`, '');

console.log(reverse('JavaScript'));

Answer 5

Answer №3

When it comes to converting arrays into strings in Javascript, the "+" operator is a key element, as explained here. To successfully achieve this conversion, I recommend initializing reverseIt with an empty string like this: reverseIt = ""; Here's a breakdown of the fourth line:

You start by adding the first character from the original string to the initially empty string reverseIt.
As you move on to the next iteration, reverseIt now holds the first character and gets concatenated with the second character from the original string.
At this stage, reverseIt would be something like str[1] + str[0].
In the subsequent iteration, the third character of str joins the existing characters in reverseIt, forming something like str[2] + str[1] + str[0].
Importantly, note that each character from the original string is added at the beginning of the reverseIt string, creating a pattern where the characters at the end of str become the characters at the front of reverseIt.
I trust this explanation clarifies the process for you.

Answer 6

When it comes to converting arrays into strings in Javascript, the "+" operator is a key element, as explained here. To successfully achieve this conversion, I recommend initializing reverseIt with an empty string like this: reverseIt = ""; Here's a breakdown of the fourth line:

You start by adding the first character from the original string to the initially empty string reverseIt.
As you move on to the next iteration, reverseIt now holds the first character and gets concatenated with the second character from the original string.
At this stage, reverseIt would be something like str[1] + str[0].
In the subsequent iteration, the third character of str joins the existing characters in reverseIt, forming something like str[2] + str[1] + str[0].
Importantly, note that each character from the original string is added at the beginning of the reverseIt string, creating a pattern where the characters at the end of str become the characters at the front of reverseIt.
I trust this explanation clarifies the process for you.

Answer 7

Answer №4

In case you were unaware, a string is essentially an array consisting of characters. It is possible to iterate through a string much like how you would with arrays, where each iteration will provide you with a single character from that particular string.

function reverseString(str) {
    var data="HELLO WORLD!";  // Test string
    var reverseIt ="";  // variable for storing reversed string
    for(var i=data.length-1;i>=0;i--) // begin the loop from the last character and move towards the first character
    {
        reverseIt +=data[i] // add current character to the reverse variable
    }
    document.write(reverseIt ); // display the reversed string
return reverseIt;
}

Answer 8

In case you were unaware, a string is essentially an array consisting of characters. It is possible to iterate through a string much like how you would with arrays, where each iteration will provide you with a single character from that particular string.

function reverseString(str) {
    var data="HELLO WORLD!";  // Test string
    var reverseIt ="";  // variable for storing reversed string
    for(var i=data.length-1;i>=0;i--) // begin the loop from the last character and move towards the first character
    {
        reverseIt +=data[i] // add current character to the reverse variable
    }
    document.write(reverseIt ); // display the reversed string
return reverseIt;
}

Is there a way to reverse a string in Javascript without using any built-in functions?

Answer №1

Answer №2

1. At the Start (i = 0)

2. In-Between (0 < i < str.length):

3. At the End (i = n - 1):

Answer №3

Answer №4

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