How to Reverse a String In-Place in JavaScript

Reverse a string in javascript without using any inbuilt function

Create a new string and add all the chars from the original string to it backwards:

function reverse1(str){
  var r = "";
  for(var i = str.length - 1; i >= 0; i--){
    r += str.charAt(i);
  }
  return r;
}

Then just say:

str = reverse1(str);

How to reverse words in a string instead of reversing the whole string?

you need to split the string by space

function reverseInPlace(str) {

  var words = [];

  words = str.match(/\S+/g);

  var result = "";

  for (var i = 0; i < words.length; i++) {

     result += words[i].split('').reverse().join('') + " ";

  }

  return result

}

console.log(reverseInPlace("abd fhe kdj"))

Reverse whole string while keeping the spaces at the same position

You just need to make following change

 //for (var i = spaces.length - 1; i >=0; i = i - 1) {
  //    array3.splice(spaces[i], 0, " ");
  //}

  for (var i = 0; i < spaces.length; i = i + 1) {
      array3.splice(spaces[i], 0, " ");
  }

You are reading spaces array in reverse but as the problem stated spaces should be at same place. Reading it from start to finish fixed the issue.

function reverseStr(input){

  var array1 = [];  

  var array2 = [];

  var nWord;

  for (var i = 0; i < input.length; i++) {

    array1.push(input[i]);

  }

  var spaces = [];

    for (var i = 0; i < array1.length; i++) {

        if(array1[i] == " ") {

            spaces.push(i);

        }

    }

  console.log(array1);

  console.log(spaces);

  array2 = array1.slice().reverse();

  var spaces2 = [];

  for (var i = 0; i < array1.length; i++) {

        if(array2[i] == " ") {

            spaces2.push(i);

        }

    }

  console.log(spaces2);

  for (var i = spaces2.length - 1; i >=0; i--) {

      array2.splice(spaces2[i], 1);

  }

  console.log(array2);

  nWord = array2.join('');

  console.log(nWord);

  var array3 = [];

  for (var i = 0; i < nWord.length; i++) {

      array3.push(nWord[i]);

  }

  console.log(array3);

  //for (var i = spaces.length - 1; i >=0; i = i - 1) {

  //    array3.splice(spaces[i], 0, " ");

  //}

  

  for (var i = 0; i < spaces.length; i = i + 1) {

      array3.splice(spaces[i], 0, " ");

  }

  console.log(array3);

  var anWord = array3.join('');

  return anWord;

}

var input = "We are farmers!";

reverseStr(input);

Reversing a string in JavaScript

reverse() is a method of array instances. It won't directly work on a string. You should first split the characters of the string into an array, reverse the array and then join back into a string:

var backway = oneway.split("").reverse().join("");

Update

The method above is only safe for "regular" strings. Please see comment by Mathias Bynens below and also his answer for a safe reverse method.

How to reverse a string in place without reversing the punctuation?

Another approach is to replace all sequences of letters with their reversed forms using replace and a regular expression, e.g.

function reverseWords(s) {

  return s.replace(/[a-z]+/ig, function(w){return w.split('').reverse().join('')});

}

document.write(reverseWords("This is fun, hopefully.")); // sihT si nuf, yllufepoh.

How to reverse a string in javascript?

Here's a working code with comments to explain you what you are doing wrong:

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
    <title>Play with Code</title>
</head>
<body>
    <form name="myform" id="form">
        Reverse String: <input type="text" id="reverseString"/><br/>
        <input type="submit" value="Submit"/>
    </form>
    <script>
        function reverseString() {
            var s = document.getElementById('reverseString').value;
            // reverse should initialized as a empty String
            // to prevent adding char to "undefined" string
            var reversed = '';

            for (var i = s.length - 1; i >= 0; i--) {
                reversed += s[i];
            }

            document.getElementById('reverseString').disabled = true;
            document.getElementById('reverseString').value = reversed;
        }

        function submit(ev) {
            // preventDefault prevent the form to do his automatic
            // behavior which submit the form with a new HTTP request
            ev.preventDefault();
            reverseString();
        }

        // Attach the event to the form
        document.getElementById('form').addEventListener('submit', submit);
    </script>
</body>
</html>

Reverse a String in JS

Arrays have a method called reverse( ). The tutorial is hinting at using this.

To convert a string into an array of characters (in reality they're just single character strings), you can use the method split( ) with an empty string as the delimiter.

In order to convert the array back into a string, you can use the method join( ) again, with an empty string as the argument.

Using these concepts, you'll find a common solution to reversing a string.

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