I work for a very technical and niche start-up as a Frontend Developer. For context, we have 3 F.E. devs and 3 B.E. devs. I was hired as a vaguely-level intermediate developer, and after about nine months at this company, my F.E. lead is advocating for me to be a Senior developer. The only issue is that the company hasn't done internal promotions before, and they're a bit stalled whilst considering how to best handle the process. There's also some ambiguity in measuring a Front-end developer's skills - especially compared to a back-end developer; Our CEO is also a seasoned back-end developer, so he understands technical skills but is unclear on how it maps to Front-end skills.
What are some things I can bring up to my company's leadership on how to measure my skills and value? Such to help facilitate a conversation around my promotion.