A jQuery 'if' condition to check multiple values

Unless there are other concerns, like if you will reuse the #test1, ... fields for more processing, yours should be good.

If you will fetch any of the values again to do something I would recommend storing the $('#test1') result in a variable so that you do not need to requery the dom.

Ex:

var t1 = $('#test1');
if((t1.val() == 'first_value')||($('#test2').val() == 'second_value') && ($('#test3').val()!='third_value')|| ($('#test4').val()!='fourth_value')) {
    t1.val('Set new value');
}

This also improves readability of the row ;)

var values = ['first_value', 'second_value', 'third_value', 'fourth_value'];
$('#test1, #test2, #test3, #test4').each(function(index, el) {
   if($.inArray(this.value, values)) {
     // do some job;
     return false; // or break;
   }
});

var c=0, b='#test', a=['first_value','second_value','third_value','fourth_value'];
for(var i=0; i<4; i++)
    if($(b+i).val() == a[i])
        c=1;
if (c) //Do stuff here

This will decrease your code size by 25 bytes;-)

Demo: just another idea is at http://jsfiddle.net/h3qJB/. Please let me know how it goes.

You can also do chaining like:

$('#test1, #test2, #test3, #test4').each(function(){ //...use this.value here  });

It might be that De Morgan's laws gives you an idea of how to make the logic a bit more compact (although I am not sure what is the specific case or is it as simple as comparing values).

Code

var boolean1 = (($('#test1').val() == 'first_value')||($('#test2').val() == 'second_value'))

var boolean2 = (($('#test3').val()!='third_value')|| ($('#test4').val()!='fourth_value'))

if (boolean1 && boolean2)
    alert("bingo");
else
    alert("buzzinga");