Node.js - method is returning UNDEFINED when parsing XML

Question

I'm parsing a hardcoded XML-structure inside a class in Node.js. The problem is that the parsing is done asynchronously, which causes the method to return the default value (null).

function Codeorder() {
    // Hardcodet XML-tree as string
    this.order = "  <root> \
                            <order instancename=\"flashlibraries\" opens=\"true\" />\
                                <order instancename=\"TESTTEST\" opens=\"true\" />\
                            <order instancename=\"flashlibraries\" opens=\"false\" />\
                        </root>";
    this.orderXML = null;
}

Codeorder.prototype.getOrderedCodepieces = function(instancename) {

    var parseString = require('xml2js').parseString;
    parseString(this.order, function (err, result) {
        return result; // This doesn't work
    });

    // Return "All OK"; 
}

module.exports = Codeorder;

How to I get the method to wait for the parser to complete and then return the XML content?

Answer 1

Disclaimer: What you want can be achieved that but it may not work with future version of xml2js.

Codeorder.prototype.getOrderedCodepieces = function(instancename) {

    var parseString = require('xml2js').parseString;
    var ret = {};
    parseString(this.order, {async: false}, function(err, data) {
      ret.err = err;
      ret.data = data;
    });
    if (ret.err) {
      throw ret.err;
    }
    return ret.data;
}

Once you have this change you can will have the data you want as the return value of getOrderedCodepieces() :

var c = new Codeorder();
var data = c.getOrderedCodepieces();
console.log(JSON.stringify(data, null, 2));

This relies on the async option of the parser being supported. As stated in the docs it may change in the future:

sync (default false): Should the callbacks be async? This might be an incompatible change if your code depends on sync execution of callbacks. Future versions of xml2js might change this