How to move all capital letters to the beginning of the string in JavaScript?

To move all capital letters to the beginning of a string in JavaScript, we can use the sort() method with a regular expression to identify uppercase letters and rearrange them.

Let's say we have the following string:

my name is JOHN SMITH

We'll use sort() along with the regular expression /[A-Z]/ to move all capital letters to the beginning of the string.

Example

var moveAllCapitalLettersAtTheBeginning = [...'my name is JOHN SMITH']
.sort((value1, value2) =>
/[A-Z]/.test(value1) ? /[A-Z]/.test(value2) ? 0 : -1 : 0).join('');
console.log("After moving all capital letters at the beginning:");
console.log(moveAllCapitalLettersAtTheBeginning);

After moving all capital letters at the beginning:
JOHNSMITHmynameis

How It Works

The solution uses the following approach:

• Spread operator (...): Converts the string into an array of individual characters
• sort() method: Sorts the array based on a custom comparison function
• Regular expression (/[A-Z]/): Tests if a character is uppercase
• Comparison logic: Returns -1 to move uppercase letters before lowercase ones
• join(''): Converts the sorted array back to a string

Alternative Method with Filter

Here's another approach using filter() to separate uppercase and lowercase characters:

function moveCapitalLettersToBeginning(str) {
    const chars = [...str];
    const uppercase = chars.filter(char => /[A-Z]/.test(char));
    const lowercase = chars.filter(char => !/[A-Z]/.test(char));
    return uppercase.join('') + lowercase.join('');
}

const result = moveCapitalLettersToBeginning('my name is JOHN SMITH');
console.log("Result:", result);

Result: JOHNSMITHmynameis 

Preserving Spaces

If you want to preserve the original spacing, you can modify the approach:

function moveCapitalLettersPreserveSpaces(str) {
    const chars = [...str];
    const uppercase = chars.filter(char => /[A-Z]/.test(char));
    const others = chars.filter(char => !/[A-Z]/.test(char));
    return uppercase.join(' ') + ' ' + others.join('');
}

const result = moveCapitalLettersPreserveSpaces('my name is JOHN SMITH');
console.log("With preserved spacing:", result);

With preserved spacing: J O H N S M I T H my name is  

Conclusion

Use the sort() method with regular expressions to rearrange string characters by case. The spread operator and join() help convert between strings and character arrays for easy manipulation.