JavaScript Program to Count the Number of Vowels in a String

The five letters a, e, i, o and u are called vowels. All other alphabets except these 5 vowels are called consonants.

Example 1: Count the Number of Vowels Using Regex

Output

Enter a string: JavaScript program
5

In the above program, the user is prompted to enter a string and that string is passed to the countVowel() function.

• The regular expression (RegEx) pattern is used with the match() method to find the number of vowels in a string.
• The pattern /[aeiou]/gi checks for all the vowels (case-insensitive) in a string. Here,
  str.match(/[aeiou]/gi); gives ["a", "a", "i", "o", "a"]
• The length property gives the number of vowels present.

Example 2: Count the Number of Vowels Using for Loop

Output

Enter a string: JavaScript program
5

In the above example,

• All the vowels are stored in a vowels array.
• Initially, the value of the count variable is 0.
• The for...of loop is used to iterate over all the characters of the string.
• The toLowerCase() method converts all the characters of a string to lowercase.
• The includes() method checks if the vowel array contains any of the characters of the string.
• If any character matches, the value of count is increased by 1.