Sum Unknown Arguments

function sumArgs (args) {
    var sum = 0;
    for (var i = 0; i < arguments.length; i++) {
        if (! isNaN(arguments[i]) ) {
            sum += parseInt(arguments[i]);
        }
    }
    return sum;
}

console.log( sumArgs(2,3,4,5,1,42,"4","f") );