jQuery make sure all form fields are filled

You cannot return false from within the anonymous function. In addition, if it did work, you would return false if your first field was empty, true if not, and completely ignore the rest of your fields. There may be a more elegant solution but you can do something like this:

function validateForm() {
  var isValid = true;
  $('.form-field').each(function() {
    if ( $(this).val() === '' )
        isValid = false;
  });
  return isValid;
}

Another recommendation: this requires you to decorate all of your form fields with that formfield class. You may be interested in filtering using a different selector, e.g. $('form.validated-form input[type="text"]')

EDIT Ah, I got beat to the punch, but my explanation is still valid and hopefully helpful.

function validateForm() {
    var invalid= 0;
    $('.form-field').each(function () {
        if ($(this).val() == '') {
            invalid++;
        }
    });

   if(invalid>0)
       return false;
   else
       return true;
}

You were returning from the inner function not from the validate method

Try

function validateForm() {
    var valid = true;
    $('.form-field').each(function () {
        if ($(this).val() === '') {
            valid = false;
            return false;
        }
    });
    return valid
}