How do I add the attribute "selected" to a drop down menu option based on that option matching some variable?

Here is how the dropdown is populated...

loginOptions = ["First", "Second", "Third];
        var Login = $( '#Login' );

        for ( var i = 0; i < loginOptions.length; i++ ) {
            Login.append('<option value="'+ loginOptions[i] +'">'+             loginOptions[i] +'</option>');
        }

I want to mark one option as "selected" based on whether or not its value matches another variable. so if loginOption[i] is equal to var existingLoginValue then set that option to 'selected'

Something that would do

if(loginOptions[i] === existingLoginValue){ print 'selected'; };

Thanks!