Check is character in javascript

How to check if a character is a letter or number in JavaScript?

To check character is a letter or number, JavaScript provides the isNaN() method just pass your character as a parameter it will check character is NaN ( Not a number ) when it returns false means the character is a number else validate the character with regex code /^[a-zA-Z]+$/ to check is a letter or not.

Today, I’m going to show How do I check if a character is a letter or number in Javascript, here I will use the javascript string isNaN() method, and regex code /^[a-zA-Z]+$/` to check if a character is a letter or number.

What is a isNaN() method?#

The isNaN() function determines whether a value is NaN or not. Because coercion inside the isNaN function can be surprising, you may alternatively want to use Number.isNaN().

What is a regex code /^[a-zA-Z]+$/ ?#

This regex code is a format of string letter, using this regex code we are able to validate character is a letter or not.

Let’s start the today’s tutorial How do you check if a character is a letter or number in JavaScript?

In the following example, we will check whether a character is a number or not using the isNaN() method when a character is a not a number we will use our regex code to check character is a letter or not.

// Example of character is a letter  const str1 = "infinitbility";  if(!isNaN(str1))  console.log('✅ character is a number') > else if(/^[a-zA-Z]+$/.test(str1))   console.log('✅ character is a letter') >  // Example of character is a Number  const str2 = "903";  if(!isNaN(str2))  console.log('✅ character is a number') > else if(/^[a-zA-Z]+$/.test(str2))   console.log('✅ character is a letter') > 

In the above program, we take example of both if string is a letter or string is a number, let’s check the output.

javascript, check if a character is a letter or number example

I hope it’s help you, All the best 👍.

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Check is character in javascript

Last updated: Jan 2, 2023
Reading time · 2 min

# Check if a Character is a Letter in JavaScript

To check if a character is a letter:

1. Compare the lowercase and the uppercase variants of the character.
2. If the comparison returns false , then the character is a letter.

Copied! 
function charIsLetter(char)  if (typeof char !== 'string')  return false; > return char.toLowerCase() !== char.toUpperCase(); > console.log(charIsLetter('a')); // 👉️ true console.log(charIsLetter('!')); // 👉️ false console.log(charIsLetter(' ')); // 👉️ false console.log(charIsLetter(null)); // 👉️ false 

If the supplied argument is not of type string, we return false right away.

We compare the lowercase and uppercase variants of the string to check if it is a letter.

This works because characters like punctuation and digits don’t have lowercase and uppercase variants.

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// 👇️ true console.log('?'.toLowerCase() === '?'.toUpperCase()); // 👇️ true console.log('1'.toLowerCase() === '1'.toUpperCase()); // 👇️ true console.log(' '.toLowerCase() === ' '.toUpperCase()); 

Comparing the lowercase and uppercase variants of a character returns false for every letter.

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// 👇️ false console.log('a'.toLowerCase() === 'a'.toUpperCase()); // 👇️ false console.log('д'.toLowerCase() === 'д'.toUpperCase()); 

# Check if a Character is a Letter using Regex

Alternatively, you can use the RegExp.test() method.

The test() method will return true if the character is a letter and false otherwise.

Copied! 
function charIsLetter(char)  if (typeof char !== 'string')  return false; > return /^[a-zA-Z]+$/.test(char); > console.log(charIsLetter('a')); // 👉️ true console.log(charIsLetter('!')); // 👉️ false console.log(charIsLetter(' ')); // 👉️ false console.log(charIsLetter(null)); // 👉️ false 

The RegExp.test method returns true if the regular expression is matched in the string and false otherwise.

The forward slashes / / mark the beginning and end of the regular expression.

The caret ^ matches the beginning of the input and the dollar sign $ matches the end of the input.

The part between the square brackets [] is called a character class and matches a range of lowercase a-z and uppercase A-Z letters.

The plus + matches the preceding item (the letter ranges) 1 or more times.

This would also work if you provide 2 or more characters.

Copied! 
function charIsLetter(char)  if (typeof char !== 'string')  return false; > return /^[a-zA-Z]+$/.test(char); > console.log(charIsLetter('a')); // 👉️ true console.log(charIsLetter('abc')); // 👉️ true 

If you only want to match a single character, remove the plus + from the regex.

Copied! 
function charIsLetter(char)  if (typeof char !== 'string')  return false; > return /^[a-zA-Z]$/.test(char); > console.log(charIsLetter('a')); // 👉️ true console.log(charIsLetter('abc')); // 👉️ false console.log(charIsLetter('')); // 👉️ false console.log(charIsLetter(null)); // 👉️ false 

You can use the i flag to make the regular expression case-insensitive. This allows you to remove the uppercase range A-Z from the square brackets.

Copied! 
function charIsLetter(char)  if (typeof char !== 'string')  return false; > return /^[a-z]+$/i.test(char); > console.log(charIsLetter('A')); // 👉️ true console.log(charIsLetter('Abc')); // 👉️ true 

The i flag allows us to do a case-insensitive search and replaces the uppercase A-Z range.

If you ever need help reading a regular expression, check out this regular expression cheatsheet by MDN.

It contains a table with the name and the meaning of each special character with examples.

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

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How To Check If A Character Is A Letter Using JavaScript

While coding in JavaScript, how do you check if a given character is a letter?

In this article, we’ll go over a couple of ways to determine this using either a regular expression matching pattern or the ECMAScript case transformation ( toLowerCase() and toUpperCase() ).

Let’s jump straight into the code!

Method 1 — Regular Expression

We’ll start with the regular expression method.

A regular expression is a sequence of characters that define a search pattern for parsing and finding matches in a given string.

In the code example below, we use both a /[a-zA-Z]/ regular expression and the test() method to find a match for the given character:

In basic terms, the /[a-zA-Z]/ regex means «match all strings that start with a letter».

If the char matches a value in the regex pattern and, therefore, is safely considered a letter from the alphabet, the test() method will return a true result. If the char value does not match the regular expression, a false value will be returned.

Here is what the method would look like inside a function:

function isCharacterALetter(char) < return (/[a-zA-Z]/).test(char) >

This method will work for characters in the English language, but won’t work for other languages like Greek or Latin. Also, this method won’t work with letters that have accents and other special characters.

When you test the function, here is what the results would look like:

console.log(isCharacterALetter("t")) // true console.log(isCharacterALetter("W")) // true console.log(isCharacterALetter("5")) // false console.log(isCharacterALetter("β")) // false console.log(isCharacterALetter("Ф")) // false console.log(isCharacterALetter("é")) // false 

Notice that special characters or other languages beyond English will not work with this method.

In the next example, we’ll go over a method that covers a wider range of languages and other non-ASCII Unicode character classes.

Method 2 — ECMAScript Case Transformation

This method will use ECMAScript case transformation ( toLowerCase() and toUpperCase() ) to check whether or not a given character is a letter.

Here is what the code looks like for this method:

char.toLowerCase() != char.toUpperCase() 

Similar to the regular expression method, this will return either a true or false value.

This method works because there are not both uppercase and lowercase versions of punctuation characters, numbers, or any other non-alphabetic characters. In other words, those characters will be identical whether or not they are uppercase or lowercase. On the contrary, letters will be different when you compare their lowercase and uppercase versions.

If you wanted to use this method in a function, here what that would look like:

function isCharacterALetter(char)

Beyond the English alphabet, this solution will also work for most Greek, Armenian, Cyrillic, and Latin characters. But, it will not work for Chinese or Japanese characters since those languages do not have uppercase and lowercase letters.

When you test the function, the results will look like this:

console.log(isCharacterALetter("t")) // true console.log(isCharacterALetter("W")) // true console.log(isCharacterALetter("5")) // false console.log(isCharacterALetter("β")) // true console.log(isCharacterALetter("Ф")) // true console.log(isCharacterALetter("é")) // true 

You’ll notice that the different languages and other non-ASCII Unicode character classes are covered using this method.

That was the last of the two methods for verifying that a character is a letter.

Thanks for reading and happy coding!

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Check If A Character Is A Letter In JavaScript

In JavaScript language, we have several ways to check if a character is a letter in JavaScript. Below we will show you how to do it with 2 methods: use the regular expression method and a combination of toLowerCase() and toUppercase() method.

How to check if a character is a letter in JavaScript

Using regular expression

In this method, to check if a character is a letter, you should learn about regular expressions first.

You can refer to the structure below:

function isCharacterALetter(char) < if (char.length !== 1) < return false; >return /[a-zA-Z]/.test(char); >

The first thing we do is we will check if char is a string by checking its number of characters via the length() method. The expression /[a-zA-Z]/ means to match all strings that start with a letter. If char matches a value in the regex pattern and is treated as a letter of the alphabet, the test() method will return a true result. A false value will be returned if the char value does not match the regular expression.

function isCharacterALetter(char) < if (char.length !== 1) < return false; >return /[a-zA-Z]/.test(char); > console.log(isCharacterALetter("a")); console.log(isCharacterALetter("b")); console.log(isCharacterALetter("6")); console.log(isCharacterALetter("32")); console.log(isCharacterALetter("Abc"));

true true false false false

Using toLowerCase() and toUppercase() methods

The toLowerCase() method converts a string to a regular string. And the toUppercase() method converts a string to uppercase.

str.toLowerCase(); str.toUpperCase();

Parameter: NONE.

Similar to the above solution, we will check if the char is a string using the length() method.

We use compare char.toLowerCase()! = char.toUpperCase() to check if the char in lowercase and uppercase are different. Because the letter can be lowercase or uppercase and the remaining characters are not case-sensitive uppercase and lowercase letters. This means that non-characters in lowercase and uppercase are identical.

function isLetter(char) < if (char.length !== 1) < return false; >return char.toLowerCase() != char.toUpperCase(); > console.log(isLetter("e")); console.log(isLetter("A")); console.log(isLetter("6")); console.log(isLetter("123")); console.log(isLetter("Hello"));

true true false false false

Summary

So, we have learned some methods to check if a character is a letter in JavaScript. It’s different. You need to know regular expressions or some string-handling functions. You should read carefully to better understand. Good luck for you!

Maybe you are interested:

My name is Tom Joseph, and I work as a software engineer. I enjoy programming and passing on my experience. C, C++, JAVA, and Python are my strong programming languages that I can share with everyone. In addition, I have also developed projects using Javascript, html, css.

Job: Developer
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