multiple functions inside of angular then()

Question

Sometimes I see more than two functions separated by comma, inside of promise then() in AngularJs. Could anyone here help to explain what the structure mean?

e.g.

then(function(response){..}, function(response){..}, function(response){..}, function(response){..});

I understand that, if there are two functions inside of then(). The first function will run if it fulfill the promise, otherwise the second will run if there is any error occurs. This structure doesn't look like chained promise either...

Thank you very much for any help here :-)

As you can learn in the docs, it's a notifyCallback.

Bergi
– Bergi

2015-10-14 16:28:33 +00:00
Commented Oct 14, 2015 at 16:28 — Bergi
– Bergi, Commented Oct 14, 2015 at 16:28

Benjamin Gruenbaum · Accepted Answer · 2015-10-14 16:29:58Z

Well:

The first function is the fulfillment handler, it will execute when the promise resolves to a value (normally).
The second function is the rejection handler, it will execute when the promise resolves with an error by rejecting (or throwing an exception in a handler).
The third function is for progress, this is a nonstandard and deprecated feature that will never be a part of ECMAScript promises - it is best to avoid it altogether since it does not compose well. It is also not supported in Angular's new $q API.
Anything past the third function passed in is ignored by the handler and will have no effect.

Here is an example for all three being called:

var good = $q.when(3);
good.then(x => console.log("Successful"));
var bad = $q.reject(Error("Bad")); // always reject with errors
bad.then(null, x => console.log("Failed"));
var d = $q.defer(); // don't do this like... ever
d.promise.then(null, null, x => console.log("Progressed"));
d.notify("event notification"); // never use this in real code ;)

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