Been working on a C++ service as part of my JavaScript developer job.
Yes, this was not a part of my job description but I took it anyway and even promised to deliver it on time.
Opportunities like this are interesting.
On the one hand, it puts a huge risk on your career if you fail to deliver on time.
On the other hand, it helps you learn a lot of things that you may not learn otherwise and earn simultaneously.
Therefore, I tend to take such opportunities once in a while.
They are great for growth and widening your knowledge in a small amount of time.
So, assess the risk and take such opportunities if they present.