Count Specific Characters from String in JavaScript | Count Vowels from String

How to count specific characters from string in JavaScript? It can be a javascript challenge question or javascript interview question where requirement can be to count number of specific characters or numbers from a given string or word or words. Write a function that finds the number of vowels in a given string.

If we have a string, we can use javascript includes method to find if it contains specific character or not. We can also loop through characters of a string using javascript for of loop. Similarly we can count number of specific characters or items from an array. But remember that its case sensitive. Using this technique, we can count number of vowel characters in a given string or we can write a function that returns the number of vowels used in a string.

Vowels are the characters ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’. To count number of vowel characters from a string,
first declare a function with a parameter. Declare a variable count with value 0. Value of count will be incremented as we find more characters. At the end this value will be returned. Function call has the argument is the string or word or words that we are counting vowel numbers from.

Declare a variable containing an array of vowels. Use for of loop. Use tolowercase method to correctly match vowels in array. For each character in the string, search for a vowel. If there’s a match, increase the count. This is one way of counting specific characters from string, in this case, vowels.

We can also use 'regular expression' or RegEx to do similar thing. Declare another function. Trigger function containing string or required text. Regular expression should match a or e or i or o or u. The "g" modifier specifies a global match. A global match finds all matches. The "i" modifier makes the match 'case insensitive'. Store the regular expression matches in the variable matches. Then return the count of matches if there is any, or return 0 if there aren't any matches. This is also a quick way to find and count specific characters from a string.

And this is how you can loop through a string or items of array to count or get specific characters.

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It can be a good javascript interview question or frontend interview question. You may not be required to solve it on paper or whiteboard but the interviewer may ask you to give an idea on how to approach this algorithm. If you have an understanding of how to solve this problem or approach this algorithm, you will be able to answer it and get your next job as a frontend developer or full-stack developer.

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