Niches = riches.

You want a super-tight thing that you do (e.g. "I fix performance issues for large NodeJS code bases", or better still "I write tooling to measure performance hotspots in NodeJS code bases".)

Despite this sounding like cutting off potential customers, it doesn't work that way. Customers will reach out to you with some generic work that they want done "because I know you know NodeJS" even when you say you specialise in something.

A good first book to read: "Book yourself Solid" by Michael Port.