Develop Reference

Else if statements with toUpperCase(), toLowerCase() and Number.isInteger() [duplicate]

How can I test if a letter in a string is uppercase or lowercase using JavaScript?

The answer by josh and maleki will return true on both upper and lower case if the character or the whole string is numeric. making the result a false result.
example using josh
var character = '5';
if (character == character.toUpperCase()) {
alert ('upper case true');
}
if (character == character.toLowerCase()){
alert ('lower case true');
}
another way is to test it first if it is numeric, else test it if upper or lower case
example
var strings = 'this iS a TeSt 523 Now!';
var i=0;
var character='';
while (i <= strings.length){
character = strings.charAt(i);
if (!isNaN(character * 1)){
alert('character is numeric');
}else{
if (character == character.toUpperCase()) {
alert ('upper case true');
}
if (character == character.toLowerCase()){
alert ('lower case true');
}
}
i++;
}

if (character == character.toLowerCase())
{
// The character is lowercase
}
else
{
// The character is uppercase
}

The problem with the other answers is, that some characters like numbers or punctuation also return true when checked for lowercase/uppercase.
I found this to work very well for it:
function isLowerCase(str)
{
return str == str.toLowerCase() && str != str.toUpperCase();
}
This will work for punctuation, numbers and letters:
assert(isLowerCase("a"))
assert(!isLowerCase("Ü"))
assert(!isLowerCase("4"))
assert(!isLowerCase("_"))
To check one letter just call it using isLowerCase(str[charIndex])

const isUpperCase = (string) => /^[A-Z]*$/.test(string)
then :
isUpperCase('A') // true
isUpperCase('a') // false

This will log true if character is uppercase letter, and log false in every other case:
var letters = ['a', 'b', 'c', 'A', 'B', 'C', '(', ')', '+', '-', '~', '*'];
​​​for (var ​i = 0; i<letters.length; i++) {
if (letters[i] === letters[i].toUpperCase()
&& letters[i] !== letters[i].toLowerCase()) {
console.log(letters[i] + ": " + true);
} else {
console.log(letters[i] + ": " + false);
}
}​
You may test it here: http://jsfiddle.net/Axfxz/ (use Firebug or sth).
​​​for (var ​i = 0; i<letters.length; i++) {
if (letters[i] !== letters[i].toUpperCase()
&& letters[i] === letters[i].toLowerCase()) {
console.log(letters[i] + ": " + true);
} else {
console.log(letters[i] + ": " + false);
}
}​
and this is for lowercase:).

function isUpperCase(myString) {
return (myString == myString.toUpperCase());
}
function isLowerCase(myString) {
return (myString == myString.toLowerCase());
}

You could utilize a regular expression test and the toUpperCase method:
String.prototype.charAtIsUpper = function (atpos){
var chr = this.charAt(atpos);
return /[A-Z]|[\u0080-\u024F]/.test(chr) && chr === chr.toUpperCase();
};
// usage (note: character position is zero based)
'hi There'.charAtIsUpper(3); //=> true
'BLUE CURAÇAO'.charAtIsUpper(9); //=> true
'Hello, World!'.charAtIsUpper(5); //=> false
See also

function isCapital(ch){
return ch.charCodeAt() >= 65 && ch.charCodeAt() <= 90;
}

More specifically to what is being asked. Pass in a String and a position to check. Very close to Josh's except that this one will compare a larger string. Would have added as a comment but I don't have that ability yet.
function isUpperCase(myString, pos) {
return (myString.charAt(pos) == myString.charAt(pos).toUpperCase());
}
function isLowerCase(myString, pos) {
return (myString.charAt(pos) == myString.charAt(pos).toLowerCase());
}

A good answer to this question should be succinct, handle unicode correctly, and deal with empty strings and nulls.
function isUpperCase(c) {
return !!c && c != c.toLocaleLowerCase();
}
This approach deals with empty strings and nulls first, then ensures that converting the given string to lower case changes its equality. This ensures that the string contains at least one capital letter according to the current local's capitalisation rules (and won't return false positives for numbers and other glyphs that don't have capitalisation).
The original question asked specifically about testing the first character. In order to keep your code simple and clear I'd split the first character off the string separately from testing whether it's upper case.

You can also use a regular expression to explicitly detect uppercase roman alphabetical characters.
isUpperCase = function(char) {
return !!/[A-Z]/.exec(char[0]);
};
EDIT: the above function is correct for ASCII/Basic Latin Unicode, which is probably all you'll ever care about. The following version also support Latin-1 Supplement and Greek and Coptic Unicode blocks... In case you needed that for some reason.
isUpperCase = function(char) {
return !!/[A-ZÀ-ÖØ-ÞΆΈ-ΏΑ-ΫϢϤϦϨϪϬϮϴϷϹϺϽ-Ͽ]/.exec(char[0]);
};
This strategy starts to fall down if you need further support (is Ѭ uppercase?) since some blocks intermix upper and lowercase characters.

There's a really simple answer, which nobody else has mentioned:
function isLowerCase(str) {
return str !== str.toUpperCase();
}
If str.toUpperCase() does not return the same str, it has to be lower case. To test for upper case you change it to str !== str.toLowererCase().
Unlike some other answers, it works correctly on non-alpha characters (returns false) and it works for other alphabets, accented characters etc.

This is straightforward, readable solution using a simple regex.
// Get specific char in string
const char = string.charAt(index);
const isLowerCaseLetter = (/[a-z]/.test(char));
const isUpperCaseLetter = (/[A-Z]/.test(char));

I believe this is the easiest solution.. You can use onchange handler in input field .. to do the validation
const isValid = e.target.value === e.target.value.toLowerCase()
if (isValid) {
//Do something
} else {
//Do something
}

With modern browsers you can use regexp and unicode property tests e.g.
/\p{Lu}/u.test("A") // is true
/\p{Lu}/u.test("Å") // is true
/\p{Lu}/u.test("a1å") // is false
More info here:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Unicode_Property_Escapes
List of general categories here:
https://unicode.org/reports/tr18/#General_Category_Property

You can also use this, it will check the string for lower and uppercase
var s = "a"
if(/[a-z]/.test(s)){
alert ('lower case true');
}
if(/[A-Z]/.test(s)) {
alert ('upper case true');
}

The best way is to use a regular expression, a ternary operator, and the built in .test() method for strings.
I leave you to Google the ins and outs of regular expressions and the test method for strings (they're easy to find), but here we'll use it to test your variable.
/[a-z]/i.test(your-character-here)
This will return TRUE of FALSE based on whether or not your character matches the character set in the regular expression. Our regular expression checks for all letters a-z /[a-z]/ regardless of their case thanks to the i flag.
So, a basic test would be:
var theAnswer = "";
if (/[a-z]/i.test(your-character-here)) {
theAnswer = "It's a letter."
}
Now we need to determine if it's upper or lower case. So, if we remove the i flag from our regular expression, then our code above will test for lower case letters a-z. And if we stick another if statement in the else of our first if statement, we can test for upper case too by using A-Z. Like this:
var theAnswer = "";
if (/[a-z]/.test(your-character-here)) {
theAnswer = "It's a lower case letter."
} else if (/[A-Z]/.test(your-character-here)) {
theAnswer = "It's an upper case letter.";
}
And just in case it's not a letter, we can add a final else statement:
var theAnswer = "";
if (/[a-z]/.test(your-character-here)) {
theAnswer = "It's a lower case letter."
} else if (/[A-Z]/.test(your-character-here)) {
theAnswer = "It's an upper case letter.";
} else {
theAnswer = "It's not a letter."
}
The above code would work. But it's kinda ugly. Instead, we can use a "ternary operator" to replace our if-else statements above. Ternary operators are just shorthand simple ways of coding an if-else. The syntax is easy:
(statement-to-be-evaluated) ? (code-if-true) : (code-if-false)
And these can be nested within each other, too. So a function might look like:
var theAnswer = "";
function whichCase(theLetter) {
theAnswer = /[a-z]/.test(theLetter) ? "It's lower case." : "";
theAnswer = /[A-Z]/.test(theLetter) ? "It's upper case." : "";
return(theAnswer);
}
The above code looks good, but won't quite work, because if our character is lower case, theAnswer gets set to "" when it test for uppercase, so lets nest them:
var theAnswer = "";
function whichCase(theLetter) {
theAnswer = /[a-z]/.test(theLetter) ? "It's lower case." : (/[A-Z]/.test(theLetter) ? "It's upper case." : "It's not a letter.");
return(theAnswer);
}
That will work great! But there's no need to have two seperate lines for setting the variable theAnswer and then returning it. And we should be using let and const rather than var (look those up if you're not sure why). Once we make those changes:
function whichCase(theLetter) {
return(/[A-Z]/.test(theLetter) ? "It's upper case." : (/[a-z]/.test(theLetter) ? "It's lower case." : "It's not a letter."));
}
And we end up with an elegant, concise piece of code. ;)

See my comment on the chosen answer. Other solutions that limit to the ASCII table or use the actual character literals completely ignore Unicode and the several hundred other characters there that have case.
This code will set the caseGroup variable to:
1 for Upper Case
-1 for Lower Case
0 for Without Case
var caseGroup = (character.toLowerCase() == character.toUpperCase() ? 0 : (character == character.toUpperCase() ? 1 : -1));
You could bake that into something like this...
function determineCase(character) {
return (character.toLowerCase() == character.toUpperCase() ? 0 : (character == character.toUpperCase() ? 1 : -1));
}
function isUpper(character) {
return determineCase(character) == 1;
}
function isLower(character) {
return determineCase(character) == -1;
}
function hasCase(character) {
return determineCase(character) != 0;
}

function solution(s) {
var c = s[0];
if (c == c.toUpperCase() && !(c >= '0' && c <= '9') &&(c >='A' && c <= 'Z')) {
return 'upper';
} else if (c == c.toLowerCase() && !(c >= '0' && c <= '9') &&(c >='a' && c <= 'z')){
return 'lower';
} else if (c >= '0' && c <= '9'){
return 'digit'
} else {
return 'other'
}
}
var str1= (solution('A')) // upper
var str2 = solution('b') // lower
var str3 = solution('1') // digit
var str4 = solution('_') // other
console.log(`${str1} ${str2} ${str3} ${str4}`)

You can test if your array has an upper case or lower case string by using the match method and regex, below is just a basic foundation to start your test
var array = ['a', 'b', 'c', 'A', 'B', 'C', '(', ')', '+', '-', '~', '*'];
var character = array.join('')
console.log(character)
var test = function(search){
upperCase = search.match(/[A-Z]/g)
console.log(upperCase)
lowerCase = search.match(/[a-z]/g)
console.log(lowerCase)
}
test(character)

This is how I did it recently:
1) Check that a char/string s is lowercase
s.toLowerCase() == s && s.toUpperCase() != s
2) Check s is uppercase
s.toUpperCase() == s && s.toLowerCase() != s
Covers cases where s contains non-alphabetic chars and diacritics.

function checkCharType (charToCheck) {
// body...
var returnValue = "O";
var charCode = charToCheck.charCodeAt(0);
if(charCode >= "A".charCodeAt(0) && charCode <= "Z".charCodeAt(0)){
returnValue = "U";
}else if (charCode >= "a".charCodeAt(0) &&
charCode <= "z".charCodeAt(0) ){
returnValue = "L";
}else if (charCode >= "0".charCodeAt(0) &&
charCode <= "9".charCodeAt(0) ) {
returnValue = "N";
}
return returnValue;
}
var myString = prompt("Enter Some text: ", "Hello world !");
switch (checkCharType(myString)) {
case "U":
// statements_1
document.write("First character was upper case");
break;
case "L":
document.write("First character was a lower case");
break;
case "N":
document.write("First character was a number");
break
default:
// statements_def
document.write("First character was not a character or a number");
break;
}
Define a Function checkCharType().By declaring the variable returnValue and initialising it to the Character "O" to indicate it's Some other value.
U for uppercase; L for Lowercase ; N for number
Use the charCodeAt() method to get the character code of the first character.
Using if Statement , which check within what range of values the character code falls.
If it falls between the character codes for A and Z, Its Uppercase,
character code between a and z ,Its Lowercase. and so on.
"A".charCode(0)
var myChar = new String("A");
myChar.charCodeAt(0);
"A" : number code "65“
Check the String

This checks the ENTIRE string, not just the first letter. I thought I'd share it with everyone here.
Here is a function that uses a regular expression to test against the letters of a string; it returns true if the letter is uppercase (A-Z). We then reduce the true/false array to a single value. If it is equal to the length of the string, that means all the letters passed the regex test, which means the string is uppercase. If not, the string is lowercase.
const isUpperCase = (str) => {
let result = str
.split('')
.map(letter => /[A-Z]/.test(letter))
.reduce((a, b) => a + b);
return result === str.length;
}
console.log(isUpperCase('123')); // false
console.log('123' === '123'.toUpperCase()); // true

This question has clearly been answered a number of times, but i thought i'd share my solution as I haven't seen it in the given answers.
var lower_case = function(letter){
lowers = "abcdefghijklmnopqrstuvwxyz";
return letter === letter.toLowerCase() && lowers.indexOf(letter) >= 0
};
var upper_case = function(letter){
uppers = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
return letter === letter.toUpperCase() && uppers.indexOf(letter) >= 0
};
2¢

function checkCase(c){
var u = c.toUpperCase();
return (c.toLowerCase() === u ? -1 : (c === u ? 1 : 0));
};
Based on Sonic Beard comment to the main answer. I changed the logic in the result:
0: Lowercase
1: Uppercase
-1: neither

Assuming that a string is only considered to not be all uppercase if at least one lowercase letter is present, this works fine. I understand it's not concise and succinct like everybody else tried to do, but does it works =)
function isUpperCase(str) {
for (var i = 0, len = str.length; i < len; i++) {
var letter = str.charAt(i);
var keyCode = letter.charCodeAt(i);
if (keyCode > 96 && keyCode < 123) {
return false;
}
}
return true;
}

I need to test against a string of any character (including white space, marks, numbers, unicode characters...). Because white space, numbers, marks... will be the same in both upper case and lower case, and I want to find real upper case letters, I do this:
let countUpperCase = 0;
let i = 0;
while (i <= string.length) {
const character = string.charAt(i);
if (character === character.toUpperCase() && character !== character.toLowerCase()) {
countUpperCase++;
}
i++;
}

Simply check the ASCII value
// IsLower verify that a string does not contains upper char
func IsLower(str string) bool {
for i := range str {
ascii := int(str[i])
if ascii < 91 && ascii > 64 {
return false
}
}
return true
}

Another way is to compare the character with an empty object, i don't really know's why it works, but it works :
for (let i = 1; i <= 26; i++) {
const letter = (i + 9).toString(36).toUpperCase();
console.log('letter', letter, 'is upper', letter<{}); // returns true
}
for (let i = 1; i <= 26; i++) {
const letter = (i + 9).toString(36);
console.log('letter', letter, 'is upper', letter<{}); // returns false
}
so in a function :
function charIsUpper(character) {
return character<{};
}
EDIT: it doesn't work with accents and diacritics, so it's possible to remove it
function charIsUpper(character) {
return character
.normalize('NFD')
.replace(/[\u0300-\u036f]/g, '')<{};
}

One I use (notice this doesnt make "TestString" as "T est String" or " Test String").
function seperateCapitalised(capitalisedString) {
if (typeof capitalisedString !== "string" || capitalisedString.length === 0)
return capitalisedString;
var newStr = capitalisedString[0];
for (var i = 1; i < capitalisedString.length; i++) {
var char = capitalisedString[i];
if (char === char.toUpperCase() && isNaN(char)) {
newStr += ' ' + char;
}
else {
newStr += char;
}
}
return newStr;
}

What does [clearString.length -1 -i]) do in an if statement

In this code, what does [clearString.length -1 -i] do ?
function palindrome(str) {
var clearString = str.toLowerCase().replace(/[^0-9a-z]/gi, '').split('');
for (var i = 0; i < clearString.length/2; i++) {
if (clearString[i] !== clearString[clearString.length -1 -i]) {
return false;
}
}
return true;
}

Actually clearString.length -1 -i calculates the index of the char that is as far from the end as i is from the beginning of the string.
Such it can be checked whether both characters are equal. If this is true for all chars you have a palindrome (read from the beginning it is the same as read from the end).

Javascript password validation at least 2 number digits [duplicate]

This question already has answers here:
Regular Expression for password validation
(6 answers)
Closed 7 years ago.
I am trying to write a javascript validation for a password with the following criteria:
Password Must:
Have exactly 8 characters
Contain letters and numbers
Contain at least two numbers
EG:
"helloo15", "1helloo5" and "h1111111" are valid, "helloo1500", "27272727"and "helloos5" are invalid.
This is what I currently have:
//Password
var pw = document.myForm.password1.value;
var Vpw = /^[a-zA-Z0-9]{8}$/;
if (!Vpw.test(pw)) {
alert("Password must be 8 digits long. It must include a maximum of two numbers.");
return false;
} else {
/* alert("Valid CCV!"); */
}
But I can't figure out how to limit it to a minimum of 2 numbers anywhere in the string. Thanks!

try this one
var pass = "some44Passddword"; //document.myForm.password1.value;
var patt = new RegExp("^(?=(.*[a-zA-Z]){1,})(?=(.*[0-9]){2,}).{8}$");
if ( !patt.test(pass) )
{
alert("Password must be 8 digits long. It must include a maximum of two numbers.");
//return false;
}
else
{
alert("Valid!");
}
you can check this here: https://jsfiddle.net/esj9go59/
UPDATE
for also avoiding non-word characters like "$%#^&" you should use
^(?!(.*[^a-zA-Z0-9]){1,})(?=(.*[a-zA-Z]){1,})(?=(.*[0-9]){2,}).{8}$
regular expression.
Please notice that for some reason javascript test function does not respect \W as non-word characters and it is better to use [^a-zA-Z0-9] instead of this as stated in comment below

I know everyone has come through here and told you to use regular expressions (partly because you started with that). Please don't. There are times in which regular expressions are the better choice. That is rare though, they are way overused, and this is not one of those times. The following code is way more readable than the regex mess in the accepted answer.
This code also allows you to test each condition individually and give customized errors to the user.
function isValidPassword(str)
{
return str.length == 8 &&
digitCount(str) >= 2 &&
hasLetters(str) &&
hasOnlyLettersAndDigits(str);
}
function isAsciiCodeLetter(asciiCode)
{
return (65 <= asciiCode && asciiCode <= 90) ||
(97 <= asciiCode && asciiCode <= 122);
}
function isAsciiCodeDigit(asciiCode)
{
return 48 <= asciiCode && asciiCode <= 57;
}
function hasLetters(str)
{
for (var i = 0, len = str.length; i < len; i++)
{
if (isAsciiCodeLetter(str.charCodeAt(i)))
return true;
}
return false;
}
function hasOnlyLettersAndDigits(str)
{
for (var i = 0, len = str.length; i < len; i++)
{
var asciiCode = str.charCodeAt(i);
if (!isAsciiCodeLetter(str.charCodeAt(i)) &&
!isAsciiCodeDigit(str.charCodeAt(i)))
{
return false;
}
}
return true;
}
function digitCount(str)
{
var count = 0;
for (var i = 0, len = str.length; i < len; i++)
{
if (isAsciiCodeDigit(str.charCodeAt(i)))
{
count++;
}
}
return count;
}
Don't use regex, but if you're dead set on using regex, match on [0-9].*[0-9] for 2 digits, [a-zA-Z] for a character, and ^[0-9a-zA-Z]{8}$ for the length and characters/digits only requirement. That's at least sort of readable:
function isValidPassword(str)
{
var atLeastTwoDigits = new RegExp("[0-9].*[0-9]");
var atLeastOneCharacter = new RegExp("[a-zA-Z]");
var onlyEightCharactersAndDigits = new RegExp("^[0-9a-zA-Z]{8}$");
return atLeastTwoDigits.test(str) &&
atLeastOneCharacter.test(str) &&
onlyEightCharactersAndDigits.test(str);
}
Test cases:
alert(isValidPassword("asdfasdf")); //false
alert(isValidPassword("asdfasd4")); //false
alert(isValidPassword("7sdfasd4")); //true
alert(isValidPassword("asdfas`f")); //false
alert(isValidPassword("asd3a4df-")); //false
alert(isValidPassword("asd3a4f-")); //false
alert(isValidPassword("asd3a4df")); //true
alert(isValidPassword("12345678")); //false
alert(isValidPassword("1helloo5")); //true
alert(isValidPassword("helloos5")); //false
alert(isValidPassword("45345345")); //false
alert(isValidPassword("123`567d")); //false

You can use another regex for that:
//This will yield FALSE (as you expect)
var pw = "1jkj3kjlkj3"
alert(pw.replace(/[^0-9]/g,"").length >= 2)
You can create a function or add that into your if.

Javascript: Validation for special characters

I'm working on some validations and can't seem to wrap my head around checking for special chars, none should be used. Currently I grab the value, make an array and check for uppercase and numbers. I need a way to check for special chars as well. Another small issue I found is that it passes an uppercase when a number is entered. Just looking for some direction on how to tackle this.
$('.tooltip').on({
focusin: function(){ //make
var top = $(this).offset().top
var left = $(this).offset().left + $(this).outerWidth()
$('.tip').remove()
$('body').append("<div class='tip' style='top:"+ top +"px;left:"+left+"px;'><div class='arrow'></div></div>")
$('.tip').animate({width: 'show', opacity: 'show'})
$(tipContent).appendTo('.tip')
},
focusout: function(){ //remove
$('.tip').fadeOut(function(){$(this).remove()})
},
keyup: function(){ if (event.keyCode == 16) return //validate
var val = $(this).val()
validate(val.split(""), val);
},
})
function validate(letters, val){
for (var i = 0; i < letters.length; i++){
if( letters[i] === letters[i].toUpperCase() ) { //uppercase check
console.log(letters[i] + ": " + 'Uppercase Passed');
}else{console.log('Uppercase Failed');
}
if( letters.length >= 9 ) { //min limit
console.log(letters[i] + ": " + 'Minimum Limit Passed');
}else{console.log('Minimum Limit Failed');
}
if( parseInt(letters[i]) > 0 ) { //number check
console.log(parseInt(letters[i]) + ' passed');
}else{console.log('at least 1 char failed');
}
}
}

An option might be to use regular expressions, which make your requirements easy to formulate:
function validate(value) {
var regex = /^[A-Z0-9]*$/; // consist only of uppercase letters and digits
var digit = /\d/; // contains a digit
if (regex.test(value) && digit.test(value) && value.length >= 9)
console.log("Test passed");
else
console.log("Test failed");
}
You even could combine them to one regex:
function validate(value) {
return /^(?=.*\d)[A-Z0-9]{9,}$/.test(value);
// | | | |
// string / | consists \ string end
// beginning | of only
// / upper alphabet letters and numbers,
// somewhere ahead at least 9 of them
// comes a digit
}
OK, if you need these steps separately, we should be able to do that. To recognice uppercase letters we just could use the regex [A-Z], but then umlauts etc wouldn't be recognized. If you handled them as special chars, we can easily use this regex:
/^(?=.*\d)(?=.*[A-Z])(?=.*[^A-Za-z0-9]).{9,}$/
| | |
digit uppercase special char
If you don't want that (or the same regexes applied as single-steps), we can test for special characters with the following condition: It is not upper- or lower-caseable, and it is not a digit.
function validation(value) {
var uc = false,
lc = false,
sc = false,
di = false,
len = value.length;
for (var i=0; i<len; i++) {
var letter = value.charAt(i),
isUpper = letter.toUppercase() == letter,
isLower = letter.toLowercase() == letter;
if (isUpper && !isLower)
uc = true;
else if (isLower && !isUpper)
uc = true;
else // isLower && isUpper - no alphabetic character
if (/\d/.test(letter))
di = true;
else
sc = true;
}
return {
someUppercase: uc,
someLowercase: lc,
someSpecial: sc,
someDigit: di,
length: len,
longEnough: len >= 9
};
}

Extracting capital letters ( English ) | Preferred method

Given a string of text
var string1 = 'IAmNotFoo';
How do you extract just the capital letters?
'IANF'
Here are some methods per links below:
function isUpperCase1(aCharacter) {
if ( ch == ch.toUpperCase() ) {
return true;
}
return false;
}
function isUpperCase2( aCharacter ) {
return ( aCharacter >= 'A' ) && ( aCharacter <= 'Z' );
}
var string1 = 'IAmNotFoo',
string2 = '',
i = 0,
ch = '';
while ( i <= string1.length ) {
ch = string1.charAt( i );
if (!isNaN( ch * 1 ) ) {
alert('character is numeric');
}
else if ( isUpperCase2() ) { // or isUpperCase1
string2 += ch;
}
i++;
}
or simply ( per comment below ):
var upper = str.replace(/[^A-Z]/g, '');
SO Related
Finding uppercase characters within a string
How can I test if a letter in a string is uppercase or lowercase using JavaScript?

The regex method is by far the simplest and most efficient, since it is just a single step as opposed to a big loop.

I like working with numbers so I would prefer converting to integers and checking the ascii range. You can see this chart here www.ascii-code.com.
All capital letters have a separate ascii code from their lower case counterparts.
do something like this
String str = "IAmNoFoo";
returnCaps(str);
Public static String returnCaps(String, str)
{
for (int i = 0; i < str.length; i++)
{
int letter = str.convertToInt(charAt(i));
if (letter >= 65 || letter <= 90)
return str.substring.charAt(i);
else
return "No Capital Letters Found"
}
}
You might need to set the loop check to i <= str.length
This will check to see if the character at each index of the string is a captial or not. I think it is easiest to think mathematically.
With a little tweaking you could very easily make this into a recursive method.