Question

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?

Answer 1

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