Error "task.apply(...).then is not a function" on node 9.7.1 about bottleneck

[SGrondin]

It's not an issue with Node 9.7.1, your code will fail on any version of Node.

From the README:

Simply put, schedule takes a function Fn and a list of arguments. Fn must return a promise. schedule returns a promise that will be executed according to the rate limits.

The function you are giving to .schedule() does not return a Promise, it returns a String.

Try this instead:

limiter.schedule(() => Promise.resolve('im the call'))
  .then((result) => { console.log('handle result', result) });

Output:

handle result im the call

Future versions of Bottleneck might wrap your non-Promise values into a Promise, or at least give a better error message.

[SGrondin]

Please reopen if the error persists 😃

[alangibson]

The dangers of late night programming 🤦‍♂️ I think just including that use of Promise in one of the examples in the README would probably be enough for people like me that tend to read the code and skim the prose.

[SGrondin]

I'll see if I can improve the Readme!

[SGrondin]

EDIT: It's no more required to return a Promise.

With the newly released 2.2.1 you'll get the following error message:

The function given to schedule() did not return a Promise. You may need to return Promise.resolve(data). You returned: This is a string (string)'

I've also added this to the Readme:

---

If your function does not return a promise, it needs to use Promise.resolve like so:

// GOOD
limiter.schedule(() => Promise.resolve("This is a string"))
.then(data => console.log(data));

// INCORRECT!
limiter.schedule(() => "This is a string")
.then(data => console.log(data));