Find div by given class and data-id

I want to find div by given class and data-id but following line doesn't work (In this example class is lesson and data-id is variable)

$('div.lesson[data-id=' + htag + ']').addClass('underline');

What am I missing?

Update

Full function looks like that

        LoadLessons(cid);
        LoadQuestions(lid);
        $('div.course[data-id=' + cid + ']').addClass('underline');
        $('div.lesson[data-id=' + lid + ']').addClass('underline');

Load.. functions are ajax calls. And class must affect content which returned by ajax call. First addclass works but second not.

Answers

Try this,

Live Demo

$('div[class=lesson][data-id="' + htag + '"]').addClass('underline');

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