How could I detect if there is an uppercase character in a string

Question

I've read countless articles about people able to detect if all characters in a string are uppercase...

function isUpperCase(str) {
    return str === str.toUpperCase();
}


isUpperCase("hello"); // false
isUpperCase("Hello"); // false
isUpperCase("HELLO"); // true

But I'm curious how I can take a string, and search to see if any characters are uppercase, and if so, return true or return a string with the characters that are uppercase.

Any help is massively appreciated, I'm trying to avoid posts on here but I couldn't find an answer that worked for me anywhere else.

Use a regular expression. `/[A-Z]/` will match an uppercase letter. — Barmar, Jun 10 '22 at 22:45
`/\p{Lu}/u` matches if the string contains any [uppercase letter](https://en.wikipedia.org/wiki/Unicode_character_property#General_Category) and will also support other languages than english. — Christopher, Jun 10 '22 at 22:59

score 11 · Accepted Answer · answered Jun 10 '22 at 22:51

11

You can use the same logic you used for all uppercase, turn the string to lowercase and if its not equal to the original string it has an uppercase letter in it.

function hasUpperCase(str) {
    return str !== str.toLowerCase();
}


console.log(hasUpperCase("hello")); // false
console.log(hasUpperCase("Hello")); // true
console.log(hasUpperCase("HELLO")); // true

answered Jun 10 '22 at 22:51

Musa

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I wish it was this easy, I keep getting errors that say that .toLowerCase is not a function – DonnyyZ Jun 11 '22 at 15:13
You must be calling the function with something that isn't a string. @DonnyyZ – Barmar Jun 12 '22 at 16:22
@Musa A perfect and consice solution – Shamoon97 Nov 16 '22 at 10:25

score 3 · Answer 2 · edited Jun 12 '22 at 10:22

3

You can use a regular expression to filter out and return uppercase characters. However, note that the naïve solution (as proposed by some of the other answers), /[A-Z]/, would detect only 26 uppercase Latin letters.

Here is a Unicode-aware regex solution:

const isAnyUpper = string => /\p{Lu}/u.test(string)

isAnyUpper('a') //    false
isAnyUpper('A') //    true
isAnyUpper('ф') //    false
isAnyUpper('á') //    false
isAnyUpper('Á') //    true

edited Jun 12 '22 at 10:22

Cody Gray - on strike

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answered Jun 10 '22 at 23:11

punund

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@CodyGray Your edit was misleading and unnecessary. This solution does not *"use a regular expression to filter out and return uppercase characters"*. – MikeM Jun 12 '22 at 14:29

score 0 · Answer 3 · answered Jun 10 '22 at 23:36

Assuming the function is only taking string of ascii letters:

function isAllUpper(str) {
    return str.split('').findIndex(ch =>  {
      const code = ch.charCodeAt(0);
      return code >= 65 && code <= 90;
    }) === -1;
}

If you want to return just the string with only the uppercase letters, then you can extend the above slightly:

function onlyUpper(str) {
    return str.split('').filter(ch =>  {
      const code = ch.charCodeAt(0);
      return code >= 65 && code <= 90;
    }).join('');
}

The assumption of ASCII-only is unrealistic. – Roland Illig Jun 12 '22 at 04:57 — Roland Illig, Jun 12 '22 at 04:57

score -2 · Answer 4 · answered Jun 10 '22 at 22:52

-2

It's as simple as:

const hasUpperCase = str => /[A-Z]/.test(str);

console.log(hasUpperCase('abcd'));
console.log(hasUpperCase('abcD'));

answered Jun 10 '22 at 22:52

MikeM

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3

It doesn't work for `Ü` and such. – Arleigh Hix Jun 10 '22 at 23:30
1

Assuming that uppercase means A-Z is as wrong as using ASCII for storing arbitrary text. Here on Stack Overflow, I expect to read high-quality, general answers. Answers assuming that English is the only language in the world don't qualify for that. – Roland Illig Jun 12 '22 at 04:54

How could I detect if there is an uppercase character in a string

4 Answers4