How to select value of dropdown using jQuery

I have a dropdown using boostrap. I need to store the value they select from the dropdown in a variable, but for now I'm just trying to print it.

window.alert($("#list_userInput_location option:selected").val());

It displays 'undefined'. If I do this:

window.alert($("#list_userInput_location option:selected").text());

It displays an empty string. Also tried this:

window.alert($("#list_userInput_location").val());

Displays 'undefined' again.

So confused.......... Any thoughts?