How to Check Case of Letter in JavaScript ?

There are different ways to check the case of the letters in JavaScript which are explained below comprehensively, one can choose the method that best suits their specific use case and requirement.

Using the function "toUpperCase()" or "toLowerCase"

Javascript has toUpperCase() and toLowerCase() methods by using these methods one can convert the string to an upper case or lower case letter and then use it to compare it with the original letter to determine the case of the letter.

Syntax:

character.toUpperCase();

Example: Demonstrating the use of the "toUpperCase()" and "toLowerCase()" methods to determine the case of the letters in JavaScript.

function checkCase(character) {
    if (character === 
    character.toUpperCase()) {
        return 'Uppercase';
    } else if (character === 
    character.toLowerCase()) {
        return 'Lowercase';
    } else {
        return 'Mixed case';
    }
}
console.log(checkCase("G"));
console.log(checkCase("g"));
console.log(checkCase("GeeksforGeeks"));

Uppercase
Lowercase
Mixed case

Using regular expression

One can use regular expressions to check whether the letters are in upper case or lower case.

Syntax:

/[A-Z]/  // Regex for only uppercase letters

Example: Demonstrating the use of the regular expression to check the case of the letter.

function checkCase(character) {
return (/[A-Z]/.test(character)) ? 'Uppercase' : 'Lowercase';
}
console.log(checkCase("G"))
console.log(checkCase("g"))

Uppercase
Lowercase

Using ASCII value

ASCII values can also be used to check the case of the letter as the ASCII values between 65 and 90 are in upper case while the ASCII values from 97 to 122 are in lower case.

Example: Demonstrating the use of ASCII to determine the case of the letter.

function checkCase(str) {
    if (str.charCodeAt(0) >= 65 && 
        str.charCodeAt(0) <= 90) {
        console.log("Letter is UppperCase")
    }
    else if (str.charCodeAt(0) >= 97 && 
        str.charCodeAt(0) <= 122) {
        console.log("Letter is in lowerCase")
    }
}

checkCase("G")
checkCase("g")

Letter is UppperCase
Letter is in lowerCase

Using localeCompare Method

The localeCompare method can be used to compare a character with its uppercase or lowercase version. Depending on the result, you can determine the case of the letter

Example: Demonstrating the use of the localeCompare method to determine the case of the letters in JavaScript.

function checkCase(character) {
    if (character.length !== 1) {
        return 'Mixed case';
    }
    
    if (character.localeCompare(character.toUpperCase()) === 0) {
        return 'Uppercase';
    } else if (character.localeCompare(character.toLowerCase()) === 0) {
        return 'Lowercase';
    } else {
        return 'Mixed case';
    }
}

console.log(checkCase("G"));  
console.log(checkCase("g")); 
console.log(checkCase("GeeksforGeeks"));

Uppercase
Lowercase
Mixed case

Using Character Comparison

In this approach we will check if character is between 'A' and 'Z' then it is Uppercase and if it's between 'a' and 'z' it is Lowercase.

Example: This example uses character Comparison to check Case of Letter.

let letter = 'g';

// Check if uppercase
if (letter >= 'A' && letter <= 'Z') {
    console.log("Uppercase");
}

// Check if lowercase
if (letter >= 'a' && letter <= 'z') {
    console.log("Lowercase");
}

Lowercase