How to use promise chaining in my coding in nodejs

Question

exports.updateMyData = function (data) {
    var resultPromise = Q.defer();
    var errorResponse = function (err) {
        resultPromise.reject(err);
    };
    findById(data.id).then(function (mydata) {
        if (!mydata) {
            errorResponse("No item found to update");
        }
        mydata.updateAttributes(data).then(function (mydata) {
            resultPromise.resolve(mydata)
        }, errorResponse)
    }, errorResponse);
    return resultPromise.promise;
};

Above coding is working fine but I want to use promise chaining for above coding. Please help me how to use?

possible duplicate of [What is the explicit promise construction antipattern and how do I avoid it?](http://stackoverflow.com/q/23803743/1048572) — Bergi, May 10 '16 at 07:35

jfriend00 · Accepted Answer · 2016-05-10T07:32:14.427

2

You can just do this:

exports.updateMyData = function (data) {
    return findById(data.id).then(function (mydata) {
        if (!mydata) {
            throw new Error("No item found to update");
        }
        return mydata.updateAttributes(data);
    });
};

or chained like this:

exports.updateMyData = function (data) {
    return findById(data.id).then(function (mydata) {
        if (!mydata) {
            throw new Error("No item found to update");
        }
        return mydata;
    }).then(function(data) {
        return mydata.updateAttributes(data);
    });
};

Note how both these options return the internal promises rather than creating a new promise. Also, a throw within a .then() handler will reject that promise automatically.

Creating a new promise like your original code was doing when you can just return the one you already have is considered a promise anti-pattern and should be avoided.

edited May 10 '16 at 07:32

answered May 10 '16 at 07:27

jfriend00

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@ppshein - On what line of code does that error occur? Are you passing `data` as an argument when you call the exported function? – jfriend00 May 10 '16 at 07:53
sorry, actual error is `mydata is not defined`. error showing `return mydata.updateAttributes(data);` that line. – PPShein May 10 '16 at 07:57
@ppshein - That's your code - I just copied from your question. You'd have to tell us what `mydata` is supposed to be. – jfriend00 May 10 '16 at 07:59
@ppshein - Do you perhaps mean it to be `data.updateAttributes(mydata)`? – jfriend00 May 10 '16 at 08:00

How to use promise chaining in my coding in nodejs

1 Answers1