Like most people here, I am a C++/Java/ObjC developer with a huge investment in existing apps and games built using C++ and Cocos2dx. Just the shift from Cocos2dx 2.x to 3.x was painful and took a lot of effort but overall it was worth it. We have been building using Cocos2dx C++ for 5+ years now, and are very happy with it.
The advantage of not having to work with multiple languages is huge for individual developers. And it becomes even more important when there are multiple people in team. Companies can deliver much better and bigger projects with smaller team sizes. Instead of hiring 2 developers each for Cocos2dx C++, Android Java, iOS ObjC and Server C# etc... and then all of them switching between different projects for their 'part' of the project etc... Now a team of 2-3 JS developers can focus on only one project and do all of it. Much more productive and economical for businesses.
It will be a slow painful shift, almost a rewrite from scratch. But it needs to be done. We have moved many of our native java/objc projects to js/cordova/ionic etc and it takes time but worth it. We haven't run into any app performance issues until now. We started working on this almost a year ago and it will take many more months for some of our projects. You can at least start the new projects in JS while you learn, and decide upon migrating existing projects later.
We are also reconsidering how and where we use cocos2d-js. There are many other js libraries like threejs which are better for some projects. But cocos2d-js is still the best option for many projects. And we are moving a lot of UI/HUD components like settings pages etc to plain html/css instead of building them with cocos2d UI components. That is 10x less code, looks better and less bugs.
And current Cocos2dx C++ is still well maintained with new features (android c++ debugging coming next) and updates so there is no rush or crisis. If you don't want to move or want to wait some more time before the trend with js is more clear, you can continue to use Cocos2dx C++ for another year or more before deciding if you need to move or not.
Good Luck to all of us