Two issues with the following statement:

$loadingIndicator = $('<div />', { 

    id: 'loading_indicator', 

    class: 'loading_indicator', 

});

1. id and class are keywords that require string delimiters if they are to be object keys according to some validators (and thus potentially some browsers).
2. The trailing comma has compatibility issues on older browsers, and isn't used elsewhere in the codebase as far as I've looked.