如何在承诺之前添加附加逻辑

Question

I use the following code which works OK, now I need to add to it before the readFileAsync another method which query the Dir, my question is how to do that ?

this is currently the code which is working

    var filePath = path.join(__dirname, '../userpath');

    return fs.readFileAsync(filePath, 'utf8')
        .then(pars.getEx.bind(null, 'user'))
        .then(process.bind(null, 'exec'))
        .then(function (result) {
            return result.stdout;
        }, function (error) {
            return error;
        });

Now I need to add some process before which is like following: which should now return the path to the readfileAsync (the -relFilePath) How should I do that

var filePath = path.join(__dirname, '../../../../employess');

fs.readdir(filePath, function (err, files) {
    files.forEach(function (file) {
        if (file.indexOf('emp1') === 0) {

            // this should be returned 
            var relFilePath = filePath + '/' + file + '/unpath.txt';

            console.log(relFilePath);
            fs.readFile(relFilePath,'utf8', function read(err, data) {
                if (err) {
                    throw err;
                }
                console.log(data);
            });
        }
    });

});

I use bluebird...

Answer 1

Just make a promise from it and chain it before the code that you already have…

var filePath = path.join(__dirname, '../../../../employess');
fs.readdirAsync(filePath)
.then(function(files) {
    for (var i=0; i<files.length; i++)
        if (file.indexOf('emp1') === 0)
            return filePath + '/' + file + '/unpath.txt';
    throw new Error("no file with emp1 found");
})
.then(function(relFilePath) {
    return fs.readFileAsync(relFilePath, 'utf8');
})
.then(pars.getEx.bind(null, 'user'))
.then(process.bind(null, 'exec'))
.then(function (result) {
    return result.stdout;
}).then(function(data) {
    console.log(data);
}, function (error) {
    console.error(error.message);
});