Threads are quite useful, and Javascript has them. However, if what you have is a computation you have the inputs to start now and won't need the result of for a while, lazy evaluation is a far more natural representation for that than a thread.

Ideally, a language ought to have one representation for lazy evaluation, not a dozen; perhaps at some point a new standard will come out that standardizes some subset of lazy evaluation that has won out. Welcome to Javascript.