Count Vowels in String

Program to count vowels in a string

BeginnerTopic: String Programs

JavaScript Count Vowels in String Program

This program helps you to learn the fundamental structure and syntax of JavaScript programming.

// Method 1: Using for loop
function countVowels1(str) {
    let count = 0;
    let vowels = 'aeiouAEIOU';
    
    for (let i = 0; i < str.length; i++) {
        if (vowels.includes(str[i])) {
            count++;
        }
    }
    return count;
}

console.log("Hello World:", countVowels1("Hello World"));

// Method 2: Using for...of loop
function countVowels2(str) {
    let count = 0;
    let vowels = ['a', 'e', 'i', 'o', 'u'];
    
    for (let char of str.toLowerCase()) {
        if (vowels.includes(char)) {
            count++;
        }
    }
    return count;
}

console.log("\nUsing for...of:", countVowels2("JavaScript"));

// Method 3: Using filter
function countVowels3(str) {
    let vowels = ['a', 'e', 'i', 'o', 'u'];
    return str.toLowerCase()
               .split('')
               .filter(char => vowels.includes(char))
               .length;
}

console.log("Using filter:", countVowels3("Programming"));

// Method 4: Using match with regex
function countVowels4(str) {
    let matches = str.match(/[aeiou]/gi);
    return matches ? matches.length : 0;
}

console.log("\nUsing regex:", countVowels4("Hello World"));

// Method 5: Using reduce
function countVowels5(str) {
    let vowels = ['a', 'e', 'i', 'o', 'u'];
    return str.toLowerCase()
               .split('')
               .reduce((count, char) => {
                   return vowels.includes(char) ? count + 1 : count;
               }, 0);
}

console.log("Using reduce:", countVowels5("Education"));

// Method 6: Count each vowel separately
function countEachVowel(str) {
    str = str.toLowerCase();
    return {
        a: (str.match(/a/g) || []).length,
        e: (str.match(/e/g) || []).length,
        i: (str.match(/i/g) || []).length,
        o: (str.match(/o/g) || []).length,
        u: (str.match(/u/g) || []).length
    };
}

console.log("\nEach vowel count:", countEachVowel("Hello World"));

Output

Hello World: 3

Using for...of: 3

Using filter: 3

Using regex: 3

Using reduce: 5

Each vowel count: { a: 0, e: 1, i: 0, o: 2, u: 0 }

Understanding Count Vowels in String

This program demonstrates different methods to count vowels in a string.

Vowels

English vowels: a, e, i, o, u (and sometimes y)

Method 1: For Loop

Traditional approach:

for (let i = 0; i < str.length; i++) {
    if (vowels.includes(str[i])) {
        count++;
    }
}

Method 2: For...Of Loop

Cleaner iteration:

for (let char of str.toLowerCase()) {
    if (vowels.includes(char)) {
        count++;
    }
}

Method 3: Filter

Functional approach:

str.toLowerCase()
   .split('')
   .filter(char => vowels.includes(char))
   .length;

Method 4: Regular Expression

Using match():

str.match(/[aeiou]/gi);

Regex Flags:

•g: Global (all matches)

•i: Case-insensitive

Method 5: Reduce

Accumulate count:

str.split('').reduce((count, char) => {
}, 0);

    return vowels.includes(char) ? count + 1 : count;

Method 6: Count Each Vowel

Individual counts:

{
    a: (str.match(/a/g) || []).length,
    e: (str.match(/e/g) || []).length,
}

    // ...

Null Safety:

•|| []: Default to empty array if no match

•Prevents error on null

When to Use:

Loop

: Simple, learning

Filter

: Functional, readable

Regex

: Concise, powerful

Reduce

: Accumulation pattern

Let us now understand every line and the components of the above program.

Note: To write and run JavaScript programs, you need to set up the local environment on your computer. Refer to the complete article Setting up JavaScript Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your JavaScript programs.

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