Do you have to build the next Facebook? Are you shooting to be an AirBnB or a Netflix or an Ebay?
Whatever you’re building, two things are non-negotiable (and they’re both about time): It’ll take more time than you think, and you’ll have to time things right. More time and better timing.
Building your JS will take more time than you think, but building everything else will take more time too. Building an audience is going to take a long time, the marketing, the customer support, the business operations, all that will take up much more time.
Trying to find product-market fit? It’s mostly a timing game. And you can put timing on your side by putting a ton of time into your idea. A ton of time now (by being in a hurry), or better, a ton of time over the long run. Because over time, the right timing will strike many times, in modest ways. Timing is like compound interest. Luck happens to those who are present.
So build something modest, and be patient.
Don’t build more JS than you can maintain over the long term. If you’re going to be building something for a long time, make sure what you are building will grow with you. Make sure you don’t depend on other people’s work too much, lest you want to keep refactoring your code when the framework you picked goes out of style.
Are you working for an immodest company? If so, focus on your skills, get good at the basics, and get good at understanding the buyer. A modest company will be happy to find you.