Nodejs: How many .then() block can you chain in a promise?

Question

Promises are a new addition to Javascript (ES6).

We can do promise chaining by appending the .then() handler to one another.

For example:

//Using MongoDB query as an example,

db.collection.findOne({id:userId})
.then()
.then()
.then()
.....
.catch(err)

So my question is how many .then() block can you have in total in a single promise?

I am thinking that perhaps it depends only on the system processing power limit. But I also wonder if there is any programmatic limitation imposed by Javascript.

Answer 1

There is no limit other than your memory, as each of them creates a new promise and a few callbacks. And notice that you are not chaining all the .then()s to a single promise, you are chaining each to the promise that the previous call returned.

Answer 2

The then method returns a Promise which allows for method chaining. When a value is simply returned from within a then handler, it will effectively return Promise.resolve(<value returned by whichever handler was called>). Hence, there is no limit. Source