Promises then/catch

Question

I have the following code:

return requestAsync({
     method: 'GET',
     url: 'https://' + servers[num - 1] + ':8033/version.txt'
}).then().catch()

I tried throwing an error in the then handler but that didn't work

If a condition is not met in the then handler, I want throw an error that the catch handler handles. How can I get that done?

Code:

var P = require('bluebird');
var defer = function () {
    var resolve, reject;
    var promise = new P(function () {
        resolve = arguments[0];
        reject = arguments[1];
    });
    return {
        resolve: function () {
            resolve.apply(null, arguments);
            return promise;
        },
        reject: function () {
            reject.apply(null, arguments);
            return promise;
        },
        promise: promise
    };
};

var pool = {maxSockets: Infinity};
var requestAsync = function (options) {
    options.pool = pool;
    options.timeout = 60000;
    options.rejectUnauthorized = false;
    options.strictSSL = false;
    var deferred = defer();
    var r = request(options, function (err, res, body) {
        if (err) {
            return deferred.reject(err);
        }
        deferred.resolve(res, body);
    });

    deferred.promise.req = r;

    return deferred.promise;
};

return requestAsync({
     method: 'GET',
     url: 'https://' + servers[num - 1] + ':8033/version.txt'
}).then(function (response) {
     throw new Error('Server is not taken');
}).catch(function (err) { });

Please show us your actual code. Where are you throwing an error? You're not even passing handlers to `then` and `catch`! — Bergi, Mar 10 '16 at 02:27
What is `requestAsync`, which promise library are you using? — Bergi, Mar 10 '16 at 02:28
Bluebird is fine normally. So what exactly is your problem, what does not work? — Bergi, Mar 10 '16 at 02:37
**Show us that code!** We can't help you otherwise. If you were doing it right, it would work. — Bergi, Mar 10 '16 at 02:44
I'd recommend to [avoid the deferred pattern](http://stackoverflow.com/a/28692824/1048572). Also notice that `resolve` only takes one argument, not multiple. Apart from that, your code seems about fine. Now what does not work? Do you see the `then` callback execute, but the `catch` callback not? Please put in some logging, and show us the output. — Bergi, Mar 10 '16 at 02:52
Eeeck, why all the code for `defer()`. That function is not needed here at all. Just use the promise that `requestAsync()` already returns. Learn how to use promises correctly and you will have far fewer problems. — jfriend00, Mar 10 '16 at 03:04
@jfriend00: The code with `defer` is *inside* `requestAsync` :-) — Bergi, Mar 10 '16 at 05:25
@Bergi - I know. I'm saying there's no reason at all to use it. I would have thought you of all people would agree with that sentiment. — jfriend00, Mar 10 '16 at 05:31
@jfriend00: A custom promisification (instead of `var requestAsync = P.promisify(reqest)`) seems to be necessary here because he wants to have a `.req` property on his promise. Of course - as I already commented - he rather should use the `Promise` constructor for this rather than a deferred. — Bergi, Mar 10 '16 at 05:36

agconti · Answer 1 · 2016-03-10T02:21:32.820

6

You can manually throw the error:

requestAsync({
 method: 'GET',
 url: 'https://' + servers[num - 1] + ':8033/version.txt'
})
.then(function () { 
  throw new Error("Catch me")
}))
.catch(function (error) {
  console.error(error)
})

jsbin: https://jsbin.com/dewiqafaca/edit?html,js,console,output

edited Mar 10 '16 at 02:21

answered Mar 10 '16 at 02:21

agconti

17,780
15
80
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1

@BrownKL it works. here's a jsbin: https://jsbin.com/dewiqafaca/edit?html,js,console,output – agconti Mar 10 '16 at 02:26

score 0 · Answer 2 · answered Mar 10 '16 at 02:20

0

Just use throw to generate a standard JavaScript exception in your then function and it should invoke the function in your catch block with whatever value you provide as the argument.

answered Mar 10 '16 at 02:20

kungphu

4,592
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Promises then/catch

2 Answers2