I'm not quite sure what you mean by "Mid Front end Devs". Do you mean not Jr and not Sr? I guess I wouldn't be quite sure how to express that either :|

I've interviewed tons of front end devs, all for product companies whose candidates are fairly different to an agency (agencies candidates with personal portfolios are likely more common). Having a portfolio at all is rare. Most anything that shows that you're active in your craft will be a plus. Github profiles are common but honestly they, on average, show near-zero public activity. Obviously there are outliers who are active in open source but my own experience shows that even very good senior devs at well-funded startups don't have much time for open source except in the rare case where a specific OS tool becomes core to their employment.

Seriously, anything that shows that you used time outside of work to create things is a plus.