Javascript is not letter

javascript isalpha – how to check if a string is alphabetic in javascript?

javascript isalpha – isAlpha. JavaScript, String, Regexp. Use RegExp.prototype.test() to check if the given string matches against the alphabetic regexp pattern.

javascript isalpha – javascript String isalpha() Method

You could just use a case – insensitive regular expression Checks if the character is an alphabetic character.

• /*/^[a-zA-Z()]*$/ – also returns true for an empty string
• /^[a-zA-Z()]$/ – only returns true for single characters.
• /^[a-zA-Z() ]+$/ – also allows spaces*/
• //better regEX to include question marks too

Example

const isAlpha = str => /^[a-zA-Z]*$/.test(str); isAlpha('pakaInfo'); // true isAlpha('welcom To pakainfo'); // false isAlpha('986565'); // false

Check if a character is alphabetic

`a`.isAlpha(); // true `i`.isAlpha(); // true `3`.isAlpha(); // false

Python String isalpha() Method

txt = "pakainfoCom" x = txt.isalpha() print(x)

isalphabetic javascript

function isAlphaOrParen(str) < return /^[a-zA-Z()]+$/.test(str); >

Javascript Function that returns true if a letter?

You can use the String.prototype.match() method along with a regular expression to check if a character is a letter or not in JavaScript. Here’s an example function that returns true if a given character is a letter:

In this function, the match() method checks whether the char parameter matches any of the lowercase or uppercase letters between a-z or A-Z respectively. If it does, it returns an array of matches, which is a truthy value. If it doesn’t match any letter, it returns null, which is a falsy value.

You can use this function to check whether a given character is a letter or not by calling it with the character as the argument. For example:

console.log(isLetter('A')); // true console.log(isLetter('a')); // true console.log(isLetter('1')); // false console.log(isLetter('%')); // false

In this example, the function returns true for the first two calls since ‘A’ and ‘a’ are letters, and false for the last two calls since ‘1’ and ‘%’ are not letters.

Isalpha, isalnum in Javascript?

In JavaScript, there are no built-in functions named isalpha() or isalnum() as they exist in some other programming languages such as Python or C++. However, you can implement similar functionality using regular expressions and the String.prototype.match() method.

isalpha(): This function is used to check if a string contains only alphabetic characters (A-Z, a-z). You can use the following regular expression to achieve this:

In this function, the ^ and $ characters match the start and end of the string, respectively. The [a-zA-Z] part matches any alphabetic character, and the + character means that the previous pattern should match one or more times. The test() method returns a Boolean indicating whether or not the given string matches the regular expression.

isalnum(): This function is used to check if a string contains only alphanumeric characters (A-Z, a-z, 0-9). You can use the following regular expression to achieve this:

In this function, the regular expression is similar to the one used in isAlpha(), except that it also includes the digits 0-9 in the pattern.

You can use these functions to check if a string contains only alphabetic or alphanumeric characters, like this:

In these examples, the functions return true if the given string contains only alphabetic or alphanumeric characters, and false otherwise.

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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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Javascript is not letter

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.

Copied! 
// 👇️ 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.

Copied! 
// 👇️ 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.

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