How to check if all inputs are not empty with jQuery

I just wanted to point out my answer since I know for loop is faster then $.each loop here it is:

just add class="required" to inputs you want to be required and then in jquery do:

$('#signup_form').submit(function(){
    var fields = $('input.required');
    for(var i=0;i<fields.length;i++){
        if($(fields[i]).val() != ''){
            //whatever
        }
    }
});

$('#form_submit_btn').click(function(){
    $('input').each(function() {
        if(!$(this).val()){
            alert('Some fields are empty');
           return false;
        }
    });
});

Just use:

$("input:empty").length == 0;

If it's zero, none are empty.

To be a bit smarter though and also filter out items with just spaces in, you could do:

$("input").filter(function () {
    return $.trim($(this).val()).length == 0
}).length == 0;

Use each:

var isValid;
$("input").each(function() {
   var element = $(this);
   if (element.val() == "") {
       isValid = false;
   }
});

However you probably will be better off using something like jQuery validate which IMO is cleaner.