AngularJS - fail resilence on $q.all()

domokun picture domokun · Dec 13, 2013 · Viewed 10.5k times · Source

I'm trying to fill some local data resolving a series of remote calls.
When every promise is resolved, I load the data and proceed.

The method $q.all( [] ) does exactly this:

        $q.all([
            this.getUserInfo(11)
                .then(function (r) {
                    results.push(r)
                }),

            this.getUserConns()
                .then(function (r) {
                    results.push(r)
                }),

            this.getUserCtxs()
                .then(function (r) {
                    results.push(r)
                })
        ])
        .then(function () {
            console.log(results)
        })


Problem is, this code is not resilient.
If any of these call fails, nobody gets the fish!

Wrapping the calls in a try/catch statement, simply causes $q.all() to entirely ignore the entry, even when not failing (note the console.log in the func)...

        $q.all([
            this.getUserInfo2(11)
                .then(function (r) {
                    results.push(r)
                }),

            function () {
                try {
                    this.getUserGroups()
                        .then(function (r) {
                            console.log(r)
                            results.push(r)
                        })
                }
                catch (err) {
                    console.log(err)
                }
            },
        ])
        .then(function () {
            console.log(results)
        })

Output:

[Object]


Any hint on how I could wrap this to be resilient?


Thanks to @dtabuenc, I've gone one step further. Implementing the error callback, I can avoid the breaking of the chain, and push the values of the resolved promises.

However, a nasty Exception is still displayed on the console... How can I get rid of that if I cannot try/catch on async requests?

Caller code

    return $q.all([

            this.getUserInfo(user_id)
                .then(function (r) {
                    results['personal_details'] = r
                }),

            this.getUserConns()
                .then(
                    function (r) {
                    results['connections'] = r
                    },
                    function(err) {
                        console.log(err)
                    })

        ])
        .then(function () {
            return (results)
        })

Callee code (inject with an exception)

    getUserConns: function() {

        return __doCall( ws.getUserConnections, {} )
            .then( function(r) {

                // very generic exception injected
                throw new Error

                if (r && r.data['return_code'] === 0) {
                    return r.data['entries']
                }
                else {
                    console.log('unable to retrieve the activity - err: '+r.data['return_code'])
                    return null
                }
            })
    },

Answer

Esailija picture Esailija · Dec 15, 2013

This will work but also push the errors to the array.

function push(r) {
    results.push(r);
}

$q.all([
    this.getUserInfo(11).then(push).catch(push),
    this.getUserConns().then(push).catch(push),
    this.getUserCtxs().then(push).catch(push)
])
.then(function () {
    console.log(results);
})

You should also improve your understanding of promises, you never should use try-catch with promises - when using promises, you use the .catch() method (with everything else being implicitly a try). This works for normal errors as well as asynchronous errors.


If you want to totally ignore the errors:

function push(r) {
    results.push(r);
}

function noop() {}

$q.all([
    this.getUserInfo(11).then(push).catch(noop),
    this.getUserConns().then(push).catch(noop),
    this.getUserCtxs().then(push).catch(noop)
])
.then(function () {
    console.log(results);
})