Transitioning library functions to utilize promises

Question

Transitioning library functions to utilize promises

converter.json2csv(MAP.fls, function (error, csv) {
    if (error) {
        return error;
    }

    file_system.writeFile(MAP.output.res, csv, function (error) {
        if (error) {
            return error;
        }
    });
});

I am currently working with the code above and I am exploring potential ways to incorporate promises for a more streamlined error handling process. The two if statements checking for errors seem redundant to me and I am wondering if there is a better approach that can be taken.

If using promises is not feasible in this scenario, are there any alternatives I could consider?

javascript bluebird

Answer 1

Answer №1

If you encounter a library with a callback interface that cannot be changed, one option is to create a wrapper function using a deferred interface:

// Here is an example of creating a wrapper module
// json2cvs.js

var Deferred = require("deferred"); // This is just for illustration purposes;
var converter = require("converter");

module.exports = function(MAP) {
    var dfd = Deferred();        

    converter.json2csv(MAP.fls, function (error, csv) {
        if (error) {
            dfd.reject(error);
        }

        file_system.writeFile(MAP.output.res, csv, function (error) {
            if (error) {
               dfd.reject(error);
            }

            // Perform some actions
            var message = "file saved";

            // Resolve on success
            dfd.resolve(message);
        });
    });

    return dfd.promise;   
}

Then, in another module, you can simply require the above module:

var json2csv = require("json2csv");

// Use the wrapper function
json2csv(input).done(function(result) {
    console.log(result);
}).fail(function(error) {
    console.log(error);
});

In this example, the deferred library used is available here.

Feel free to explore and use other deferred libraries as well.

Answer 2

If you encounter a library with a callback interface that cannot be changed, one option is to create a wrapper function using a deferred interface:

// Here is an example of creating a wrapper module
// json2cvs.js

var Deferred = require("deferred"); // This is just for illustration purposes;
var converter = require("converter");

module.exports = function(MAP) {
    var dfd = Deferred();        

    converter.json2csv(MAP.fls, function (error, csv) {
        if (error) {
            dfd.reject(error);
        }

        file_system.writeFile(MAP.output.res, csv, function (error) {
            if (error) {
               dfd.reject(error);
            }

            // Perform some actions
            var message = "file saved";

            // Resolve on success
            dfd.resolve(message);
        });
    });

    return dfd.promise;   
}

Then, in another module, you can simply require the above module:

var json2csv = require("json2csv");

// Use the wrapper function
json2csv(input).done(function(result) {
    console.log(result);
}).fail(function(error) {
    console.log(error);
});

In this example, the deferred library used is available here.

Feel free to explore and use other deferred libraries as well.

Transitioning library functions to utilize promises

Answer №1

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