Wrap in promise JavaScript generic function

This question already has an answer here:

How do I convert an existing callback API to promises? 17 answers

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for example we can use Q libary and defer, something like this:

run: function (req, res, filePath) {
        var d = Q.defer();

        var writeStream = fs.createWriteStream(fileRelPath, {flags: 'w'});
        req.pipe(writeStream);
        req.on("end", function () {
            console.log("Finish to update data file");
            d.resolve();
        });

        req.on("error", function (err) {
            d.reject(err);
        });



        return d.promise.then(function(){
            res.end("File " + filePath + " saved successfully");
        }).catch(function(err){
            //handle error
        })
    }

In this code promise will resolve after req end event, and then res.end, but I recommend create another method for finish response and work with promise from method run. Good luck!

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