"Cannot call method 'then' of undefined" when specifying an invalid .catch filter

[joepie91]

I've written the following code (Coffeescript):

Promise.try ->
    req.model("AuditLogEntry").getAll([], start: start, limit: limit, require: yes)
.catch req.db.EmptyResponse, (err) ->
    throw util.NotFound()
.then (entries) ->
    res.send entries.json()

... and I made the mistake of trying to filter by req.db.EmptyResponse (which was undefined) rather than by the correct attribute req.db.EmptyError. However, bluebird didn't remark on me passing undefined as filter - instead, it gave me the following error:

TypeError: Cannot call method 'then' of undefined
    at module.exports (/home/sven/projects/anonnews3/routes/audit-log.js:27:6)
    at handleReturn (/home/sven/projects/anonnews3/node_modules/express-promise-router/lib/express-promise-router.js:27:27)
    at Object.handle (/home/sven/projects/anonnews3/node_modules/express-promise-router/lib/express-promise-router.js:55:9)
    at next_layer (/home/sven/projects/anonnews3/node_modules/express/lib/router/route.js:103:13)
    [...]

This refers to the .then call in line 5 of the code snippet above. Instead of throwing a fairly cryptic error (why does .catch return undefined?), it should probably throw an error of some sort that the specified filter is invalid - after all, it's not an Error type nor a function.

[petkaantonov]

You are right, I think it should just throw synchronously

[benjamingr]

Not sure I'm particularly fond of the idea of this promise returning function throwing synchronously.

However, it's consistent with what the promise constructor does and it's a core library method rather than an API.

[domenic]

Noooooooo

[petkaantonov]

Domenic it's very comparabale to syntaxerror, like you would never have a runtime dynamic value as a catch predicate. Or would you?

[domenic]

You very well could, e.g. I could imagine some form validation code composing its filter.

In general .then and .catch should never throw. I think it's a mistake that new Promise can do so but I let that one slip through :-/.

It should just return a promise rejected with a TypeError IMO.