How to count vowels in a Javascript string with two functions?

Question

I'm trying to write a Javascript function that counts the vowels in a string by calling another function inside that function, but when I test it in the console it returns 0.

Here is my first function that works fine and recognizes if a string is a vowel:

function isVowel(ch){
    var pattern = /[aeiouAEIOU]/
    return pattern.test(ch);
};

For the second function none of my ideas have worked. Here are a few examples of what I have tried so far:

This one returns me a 0:

function countVowels(str){
var count = 0;

for(var i; i <= str.length; ++i){
    if(isVowel(i)){
        ++count;
    }
}
return count;
};

I also tried the above, but removing the .length after str in the for() area.

Another example, but this one gives me an error:

function countVowels(str){
var count = 0
var pattern = /[aeiouAEIOU]/

for(var i = 1; i <= str.length(pattern); ++i){
    if(isVowel(i)){
        ++count;
    }
}
return count;
};

I've tried various other functions as well, but for the sake of keeping this post relatively short I won't continue to post them. I'm quite new to Javascript and I'm not sure what I'm doing wrong. Any help would be greatly appreciated!

"This one returns me a 0" - of course it does, because you are only passing the loop counter i to isVowel - so you are checking whether 0 is a vowel, 1 is a vowel, etc. Numbers aren't vowels, so the result is of course 0. — C3roe
– C3roe, Commented Oct 28, 2016 at 21:58

Robiseb · Accepted Answer · 2016-10-28 22:06:02Z

1

Try using .match() with the g attribute on your String.

g: global
i: case insensitive

Regexp documentation

function countVowels(ch){
  return ch.match(/[aeiouy]/gi).length;
}

var str = "My string";
alert(countVowels(str)); // 2

edited Oct 28, 2016 at 22:06

answered Oct 28, 2016 at 21:53

Robiseb

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Comments

David · Accepted Answer · 2016-10-28 22:25:02Z

Although Robiseb answer is the way to go, I want to let you know why you code is not working (I'm referring your first attempt). Basically you made two mistakes in the loop:

As CBroe stated, you are passing i to your isVowel function. i is a integer representing the index of the loop, not the actual character inside the string. To get the character you can do str.substr(i, 1), what means "give me one character from the position i inside the string".
You are not giving a initial value to the i variable. When you create a variable, it is undefined, so you can not increment it.

alert(countVowels("hello"));

function countVowels(str) {
  var count = 0;

  for (var i = 0; i <= str.length; ++i) {
    if (isVowel(str.substr(i, 1))) {
      count++;
    }
  }
  return count;
};

function isVowel(ch) {
  var pattern = /[aeiouAEIOU]/
  return pattern.test(ch);
};

UPDATE: You will see that other answers use other methods to select the character inside the string from the index. You actually have a bunch of different options. Just for reference:

str.slice(i,i+1);
str.substring(i,i+1);
str.substr(i,1));
str.charAt(i);
str[i];

Barmar · Accepted Answer · 2016-10-28 22:00:50Z

0

i is the index, not the character. It should be:

if (isVowel(str[i])) {
    count++;
}

Also, str.length(pattern) is wrong. length is a property, not a function, so it should just be str.length.

answered Oct 28, 2016 at 22:00

Barmar

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Comments

Community · Accepted Answer · 2017-05-23 10:27:28Z

0

You forgot to assign the value 0 to i variable

And parameter for isVowel is the character, not the index of string

Here information about the JS language: https://stackoverflow.com/tags/javascript/info

function isVowel(ch){
    var pattern = /[aeiouAEIOU]/
    return pattern.test(ch);
}

function countVowels(str){
var count = 0;

  // you forgot to assign the value to i variable
for(var i = 0; i < str.length; i++){

  // isVowel(str[i]), not isVowel(i)
    if(isVowel(str[i])){
        count++;
    }
}
return count;
}

console.log(countVowels('forgot'))

edited May 23, 2017 at 10:27

CommunityBot

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answered Oct 28, 2016 at 22:03

A A

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Comments

sorpigal · Accepted Answer · 2016-10-28 22:09:46Z

0

Obviously you should do it this way:

function isVowel(c){
    var lc = c.toLowerCase();
    if(lc === 'y'){
        return (Math.floor(Math.random() * 2) == 0);
    }
    return ['a','e','i','o','u'].indexOf(lc) > -1;
}
function countVowels(s){
    var i = 0;
    s.split('').each(function(c){
        if(isVowel(c)){
            i++;
        }
    });
    return i;
}
console.log(countVowels("the quick brown fox jumps over the lazy dog"));

Which, although less efficient and less useful than other answers, at least has the entertaining property of returning a different count 50% of the time, because sometimes Y.

answered Oct 28, 2016 at 22:09

sorpigal

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