I just don’t get the class/prototype approach, honestly. It really seems to me that you get almost all of the benefits and more by just returning an object from a closure, which has the extra benefits of encapsulation and using only simple language features that a JS user pretty much has to use at some point:

    const createCounter = ({ startAt = 0, incremementBy = 1 }) => {
      let count = startAt
      return {
        currentCount: () => count,
        step: () => {
          count += incremementBy
        }
      }
    }

    const counter = createCounter({ startAt: 5 })
    counter.step()

versus

    class Counter {
      constructor({ startAt = 0, incrementBy = 1 }) {
        this.startAt = startAt
        this.incrementBy = incrementBy
        this.count = 0
      }

      step() {
        this.count += this.incrementBy
      }
    }

    const counter = new Counter({ startAt: 5 })