JavaScript Program To Reverse A String - Programiz

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JavaScript Program to Reverse a String

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

  • JavaScript String
  • JavaScript Function and Function Expressions

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 position of 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.

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