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JavaScript - check if character is letter
18 points
In this short article, we would like to show how to check if the character is a letter using JavaScript.
Hint: in the below example you will find a solution that has support for i18n for many alphabets.
It is like
\wregular expression group with i18n characters.
Quick solutions:
xxxxxxxxxx1
const isLetter = (character) => {2
// it will work only for: most Latin, Greek, Armenian and Cyrillic scripts.3
// it will not work for: Chinese, Japanese, Arabic, Hebrew and most other scripts.4
return character && character.length === 1 && character.toLowerCase() !== character.toUpperCase();5
};or:
xxxxxxxxxx1
const LETTER_EXPRESSION = /^\p{L}$/u; // Supported by ES6+, Some bugs in FF < 782
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const isLetter = (character) => {4
return character && LETTER_EXPRESSION.test(character);5
};
Important things:
- by default, only modern JavaScript (ES6+) introduces some solutions to check if some character is a letter,
- if ES6+ is not supported, it is possible to use case conversion to make some letter detection - it doesn't work in all cases but can be enough,
- the third option is to use an external library: XRegExp or unicode-properties (with
getCategory()) - but it increases bundle size, what not accepted on some websites.
In this section, you will find a function that gives good enough support for many letters detection.
xxxxxxxxxx1
let isLetter;2
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try {4
// Unicode expression:5
const LETTER_EXPRESSION = /^\p{L}$/u; // Supported by ES6+, Some bugs in FF < 786
isLetter = (character) => {7
return character && LETTER_EXPRESSION.test(character);8
};9
} catch(e) {10
// Case conversion (legacy):11
console.log('Unicode flag in regular expressions are not supported. Used legacy isLetter() function.');12
isLetter = (character) => {13
// it doesn't work for some alphabets but still enough in most cases14
return character && character.length === 1 && character.toLowerCase() !== character.toUpperCase();15
};16
}17
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// Usage example:20
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//Note: Unicode expression is supported by modern Chrome, Safar, Edge, FF22
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// // Unicode expression | Case conversion (legacy)24
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// letters26
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console.log(isLetter('é')); // true | true28
console.log(isLetter('è')); // true | true29
console.log(isLetter('ê')); // true | true30
console.log(isLetter('ü')); // true | true31
console.log(isLetter('ö')); // true | true32
console.log(isLetter('à')); // true | true33
console.log(isLetter('a')); // true | true34
console.log(isLetter('z')); // true | true35
console.log(isLetter('A')); // true | true36
console.log(isLetter('Z')); // true | true37
console.log(isLetter('日')); // true | false38
console.log(isLetter('я')); // true | true39
console.log(isLetter('דֹ')); // false | false40
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// digits42
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console.log(isLetter('0')); // false | false44
console.log(isLetter('5')); // false | false45
console.log(isLetter('9')); // false | false46
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// other48
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console.log(isLetter('10')); // false | false50
console.log(isLetter('ab')); // false | false51
console.log(isLetter('😎')); // false | false52
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console.log(isLetter('-')); // false | false54
console.log(isLetter('.')); // false | false55
console.log(isLetter('+')); // false | false56
console.log(isLetter('*')); // false | false
