JavaScript function to return a decimal digit at specific position (0-indexed, from the end) of a given number.

digitAtSpecifiedPosition.js

/**
 * Returns a given power of ten (10 ^ 0 = 1, 10 ^ 1 = 10, 10 ^ 2 = 100, etc.).
 */
function powerOfTen( power ) {
    var result = 1;
    for ( i = 0; i < power; i++ ) {
        result *= 10;
    }
    return result;
}

/**
 * Returns a digit at specific position (0-indexed, from the end) of a given number. For example:
 * - a first digit of 5 is 5
 * - a first digit of 15 is 5
 * - a second digit of 15 is 1
 * - a third digit of 215 is 2
 * - a third digit of 15 is 0 (it does not exist)
 * - a second digit of 5 is 0 (does not exist either)
 */
function getDigitAtPosition( integer, position ) {
    var positionInBase10 = powerOfTen( position );
    var nextPositionInBase10 = powerOfTen( position + 1 );
    return ( integer % nextPositionInBase10 - integer % positionInBase10 ) / positionInBase10;
}

alert( getDigitAtPosition( 1234, -1 ) == 0 );
alert( getDigitAtPosition( 1234, 0 ) == 4 );
alert( getDigitAtPosition( 1234, 1 ) == 3 );
alert( getDigitAtPosition( 1234, 2 ) == 2 );
alert( getDigitAtPosition( 1234, 3 ) == 1 );
alert( getDigitAtPosition( 1234, 4 ) == 0 );