var $foo = $('li');
var $baz = $('#baz1');
console.log('Index: ' + $foo.index($baz)); // 2
var $tests = $(".test");
var $bar = $("#bar1");
// implicitly calls .first() on the argument
console.log('Index: ' + $tests.index($bar)); // 1
console.log('Index: ' + $tests.index($bar.first())); // 1