How would I write a JavaScript function that detects if the user is typing in all-caps in a <textarea>, and disallow submitting of the form until the offender has corrected their text? Understandably, a definition of all-caps is up for some debate, but here's what I'm aiming to achieve:

• YOU CAN'T DO THAT. IT'S NOT SMART. is obviously what I'm trying to snake out, because it's obnoxious.
• I like this this school. is acceptable because single letter "all capital" words are a part of the English language.
• I mean, COME ON! This is ridiculous! should this be acceptable? In a text field that doesn't support rich text, a user needs to be able to express emphasism. I think this should be acceptable.

Anyone have any suggestions? I imagine a regex is in order.

How would I write a JavaScript function that detects if the user is typing in all-caps in a <textarea>, and disallow submitting of the form until the offender has corrected their text? Understandably, a definition of all-caps is up for some debate, but here's what I'm aiming to achieve:

• YOU CAN'T DO THAT. IT'S NOT SMART. is obviously what I'm trying to snake out, because it's obnoxious.
• I like this this school. is acceptable because single letter "all capital" words are a part of the English language.
• I mean, COME ON! This is ridiculous! should this be acceptable? In a text field that doesn't support rich text, a user needs to be able to express emphasism. I think this should be acceptable.

Anyone have any suggestions? I imagine a regex is in order.

• javascript
• regex

• Probably you got to look for ASCII chars > 95. – Abilash Commented May 26, 2013 at 3:18
• 3 Maybe just set a threshold for the percent of uppercase characters permitted? No more than 50%? I think the answer won't be hard once you specify the problem more precisely. – Dave S. Commented May 26, 2013 at 3:21
• Your definition still isn't exact enough. How would you measure that? At most n words in caps allowed? – bfavaretto Commented May 26, 2013 at 3:22
• I'm not sure defining a threshold is appropriate, because the user could essentially type every second word in all caps and maintain the under 50% threshold, no? I think there needs to be some sort of logic applied – Jody Heavener Commented May 26, 2013 at 3:24
• 1 If the text area contains NO lower-case letters, and it contains ANY upper-case letters, then it's all-caps. The second check avoids plaining if the field is just numbers (although that seems unlikely for a textarea. – Barmar Commented May 26, 2013 at 3:33

3 Answers 3

Javascript function for checking that a string has uppercase letters but no lowercase letters:

function allCaps(word) {
    var containsUpper = /[A-Z]/.test(word);
    var containsLower = /[a-z]/.test(word);

    return containsUpper && !containsLower;
}

I suggest getting a ratio of uppercased letters. Here is a way:

function getCapsRatio(val) {
    // Get the number of uppercase letters
    var up = (val.match(/[A-Z]/g) || '').length,

    // Get the number of letters (no space)
        fullLetters = (val.match(/[^\s+]/g) || '').length;

    // So the ratio of uppercase letters pared to downcase is...
    return (up * 100) / fullLetters;
}

So you'd use this function like this:

var ratio = getCapsRatio(value);
if (ratio > 50) {
    // 50% of uppercase letters? this guy is all caps!
}

This should be studied, but I guess 50% is a good ratio to think the guy is all caps.

Perhaps simply this this :

 /[a-z]/i.test(str) && str.toUpperCase () == str

Compare the original string with itself up-cased, if equal then user has typed only upper-case letters.