randomString = function(target, min_length = 16) {
    var chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz';
    var string_length = min_length;
    var randomstring = '';
    for (var i = 0; i < string_length; i++) {
        var rnum = Math.floor(Math.random() * chars.length);
        randomstring += chars.substr(rnum, 1);
    }
    var regex = new RegExp(/^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*\d)[a-zA-Z\d]{8,}$/);
    if(!regex.test(randomstring)){
        randomString();
    }else{
        elm = document.getElementById(target);
        $(elm).val(randomstring);
    }    
}