Node object assignment in asynchronous callback function hanging indefinitely

Question

I'm implementing a Github Commit History Flow Visualizer in Angular with a Node backend handling webhooks and sockets. I'm using the node package deferred to handle promises and I'm running into some trouble assigning complex variables inside my function callbacks. I love promises, but this one is stumping me. See my code below:

function getGithubRepoData(repoName) {
    var d = deferred();

    var reponseData = {
        branches: { values: [] },
        tags: { values: [] },
        commits: [{ values: [] }]
    }

    deferred(getGithubRepoBranches(repoName), getGithubRepoTags(repoName))(function(result) {
        console.log("both done");
        console.log(result[0]);
        console.log("blocking?");
        responseData.branches.values = result[0];
        console.log("past here?");
        responseData.tags.values = result[1];
        console.log("now do commits");
        getGithubRepoCommits(repoName, result[0]).then(function(result) {
            responseData.commits[0].values = result;
            d.resolve(responseData);
        })
    })
    return d.promise();
}

This function is clearly meant to get the branches, tags, and commits (for all branches). The problem lies in when I try to assign responseData.branches.values. The code executes properly until then and just hangs, outputting the following:

both done
4
blocking?

And then nothing...

Here's a simpler proof of concept you can run to illustrate my issue:

var deferred = require('deferred'); 

function dtest() {
    var d = deferred();
    setTimeout(function () {
        d.resolve("good");
    }, 500);
    return d.promise;
}

var reponseData = {
    branches: { values: [] },
    tags: { values: [] },
    commits: [{ values: [] }]
}
var tester = "test";
deferred(dtest())(function(result) {
    tester = result;
    console.log(result);
    console.log("here?");   
    responseData.branches.values = result;
    console.log("here?");
    console.log(responseData.branches.values);
})

Which outputs:

good
here?

As you can see, the simple string variable is assigned with no issue, but the more complex object hangs indefinitely.

At this point my suspicion is that the package I am using has some error that I'm not seeing, but I'm hoping someone with more Node knowledge than me can swoop in and point out where I'm falling into a locking issue or some race condition. If this doesn't work I'll have to look into running each get function in order instead of parallel. Thanks in advance for the help!

In your standalone example, you always resolve "good" - this promise is probably swallowing the error when responseData.branches.values is undefined. Edit: Please see the "ending chain" section for error catching/handling. https://github.com/medikoo/deferred/blob/master/README.md — Sean Ryan, May 05 '16 at 22:17
Avoid the [deferred antipattern](http://stackoverflow.com/q/23803743/1048572)! — Bergi, May 05 '16 at 22:56

score 1 · Accepted Answer · answered May 05 '16 at 22:40

1

In your first code piece you have responseData misspelled "reponseData". reponseData was then undefined later. You are not catching the error thrown from within the deferred promise, so it appears to hang.

answered May 05 '16 at 22:40

Sean Ryan

438
4
11

Never before have I gone to such lengths do discover a typo. Good grief. Thanks man. – nashter May 06 '16 at 02:35

Node object assignment in asynchronous callback function hanging indefinitely

1 Answers1