JavaScript Program to Reverse a String

In this tutorial, you will learn to write a JavaScript program that reverses a string.

To understand this example, you should have the knowledge of the following JavaScript programming topics:


Example 1: Reverse a String Using for Loop

// program to reverse a string

function reverseString(str) {

    // empty string
    let newString = "";
    for (let i = str.length - 1; i >= 0; i--) {
        newString += str[i];
    }
    return newString;
}

// take input from the user
const string = prompt('Enter a string: ');

const result = reverseString(string);
console.log(result);

Output

Enter a string: hello world
dlrow olleh

In the above program, the user is prompted to enter a string. That string is passed to the reverseString() function.

Inside the reverseString() function,

  • An empty newString variable is created.
  • The for loop is used to iterate over the strings. During the first iteration, str.length - 1 gives the last element. That element is added to the newString variable.
    This process continues for all the string elements.
  • The value of i decreases in each iteration and continues until it becomes 0.

Example 2: Reverse a String Using built-in Methods

// program to reverse a string

function reverseString(str) {

    // return a new array of strings
    const arrayStrings = str.split("");
   
    // reverse the new created array elements
    const reverseArray = arrayStrings.reverse();
 
    // join all elements of the array into a string
    const joinArray = reverseArray.join("");
    
    // return the reversed string
    return joinArray;
}
 
// take input from the user
const string = prompt('Enter a string: ');

const result = reverseString(string);
console.log(result);

Output

Enter a string: hello
olleh

In the above program, the built-in methods are used to reverse a string.

  • First, the string is split into individual array elements using the split() method. str.split("") gives ["h", "e", "l", "l", "o"].
  • The string elements are reversed using the reverse() method. arrayStrings.reverse() gives ["o", "l", "l", "e", "h"].
  • The reversed string elements are joined into a single string using the join() method. reverseArray.join("") gives olleh.