how to check if this class is present in html code example

Example 1: jquery check if a class exists

if ($(".mydivclass")[0]){
    // Do something if class exists
} else {
    // Do something if class does not exist
}

Example 2: jquery select input value empty and hasclass

$('.check-fields').on('click', function () {

    var reqlength = $('.required-entry').length;
    console.log(reqlength);
    var value = $('.required-entry').filter(function () {
        return this.value != '';
    });

    if (value.length>=0 && (value.length !== reqlength)) {
        alert('Please fill out all required fields.');
    } else {
        alert('Everything has a value.');
    }
});