nodejs event stream setting a variable per stream

Question

I have a code that creates a readable stream . I would like to set the name of the stream in the getStream method . I tried setting a property as shown below . I am able to access the property in the onceFunction but I am not able to access the property in the map Function . Let me know what I am doing wrong

var onceFunction = function(str1,record) {
    console.log("OnceFunction",this.nodeName);
}
var getStream = function(csvData) {
    var dirNames = csvData.split("/");
    var nodeName = dirNames[dirNames.length-2];
    var fileName = csvData;
    stream = fs.createReadStream(csvData);
    stream.nodeName = dirNames[dirNames.length-2];

    return stream;
};
var myFileList = ["D:\mypath\file"];

for ( var i = 0; i< myFileList.length; i++ ) {
    getStream(myFileList[i])
        .once('data',onceFunction)
        .pipe(es.split())
        .on('end',endFunction)
        .pipe(es.map(function(data,cb) {
            console.log(this.nodeName);

        }));
}

Answer 1

Because "es" has it's own "this". And passes it to es.map callback. Where, ofcource, nodeName is empty. Refactor you code to use closures and avoid using "this". For example in pseudocode:

for ( var i = 0; i< myFileList.length; i++ ) {
    processFile(myFileList[i]);
}

var processfile = function(file) {
    var stream = getStream(file);
    var somevar = stream.nodeName;
    stream.once('data',onceFunction)
        .pipe(es.split())
        .on('end',endFunction)
        .pipe(es.map(function(data,cb) {
            console.log(somevar);
            console.log(stream.nodeName);
        }));
}