Problem

As you probably have noticed during your node.js development, it is really easy to get deep into callback mess. Consider the following code:

var fs = require('fs');

fs.readFile('/etc/passwd',
    function(err, data) {
        if (err) {
            handleError(err);
            return;
        }

        fs.writeFile('myPwdCopy.txt',
            function(err) {
                if (err) {
                    handleError(err);
                }

                fileCopiedCallback();
            }
        );
    }
);

Here we just copied a file from one place to another, and yet we already have three levels of folding.

Solution

Node-chain is perhaps a naive attempt to solve this problem. Consider the solution:

var fs = require('fs'),
    runChain = require('node-chain').runChain,
    chain = [

        // Step 1: call fs.readFile and pass the 'data' as argument
        {
            target: fs.readFile,
            args: ['/etc/passwd'],
            errorHandler: handleErrors,
            passResultToNextStep: true
        },

        // Step 2: call fs.writeFile
        {
            target: fs.writeFile,
            errorMessage: 'Unable to write the file'
        }
    ];

runChain(chain);