Problem Nineteen

nineteen.js

var date,
    counter = 0;

for (var i = 1901; i <= 2000; i++) {
    for (var j = 1; j <= 12; j++) {
        date = new Date( i + '-' + pad( j ) + '-01' );
        if ( date.getDay() === 0 ) {
            counter++;
        }
    }
}

function pad( string ) {
    string += '';
    if ( string.length === 1 ) {
        string = '0' + string;
    }
    return string;
}

document.write( counter );