Strange node.js error: TypeError: Object #<Object> has no method 'on'

Question

I'm trying to run a simple screen scraping app in node.js. The code is posted here: https://github.com/anismiles/jsdom-based-screen-scraper http://anismiles.wordpress.com/2010/11/29/node-js-and-jquery-to-scrape-websites/

The server starts up fine, but then when I run a query on it, I get the following error. Does anyone know why that is?

TypeError: Object #<Object> has no method 'on'
    at Object.<anonymous> (/Users/avishai/Downloads/anismiles-jsdom-based-screen-scraper-f0c79d3/searcher-server.js:9:10)
    at param (/Users/avishai/.node_libraries/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:146:21)
    at param (/Users/avishai/.node_libraries/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:157:15)
    at pass (/Users/avishai/.node_libraries/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:162:10)
    at Object.router [as handle] (/Users/avishai/.node_libraries/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:168:6)
    at next (/Users/avishai/.node_libraries/.npm/connect/0.5.10/package/lib/connect/index.js:218:15)
    at Server.handle (/Users/avishai/.node_libraries/.npm/connect/0.5.10/package/lib/connect/index.js:231:3)
    at Server.emit (events.js:45:17)
    at HTTPParser.onIncoming (http.js:1078:12)
    at HTTPParser.onHeadersComplete (http.js:87:31)

The function that appears to be throwing the error is:

function books(app){
    app.get('/:query', function(req, res, next) {

        res.writeHead(200, { 'Content-Type': 'text/html' });

        var rediff = require('./searcher-rediff');
        rediff.on('on_book', function(item){
            res.write(item + "<br/>");
        });
        rediff.on('completed', function(){
            res.end();
        });
        rediff.search(escape(req.params.query));

    });
}

UPDATE

Now I noticed that on the first request, I get this:

SyntaxError: Unexpected strict mode reserved word
    at Module._compile (module.js:369:25)
    at Object..js (module.js:380:10)
    at Module.load (module.js:306:31)
    at Function._load (module.js:272:10)
    at require (module.js:318:19)
    at Object.<anonymous> (/Users/avishai/Downloads/anismiles-jsdom-based-screen-scraper-f0c79d3/searcher.js:2:15)
    at Module._compile (module.js:374:26)
    at Object..js (module.js:380:10)
    at Module.load (module.js:306:31)
    at Function._load (module.js:272:10)

Answer 1

The only explanation that comes to mind is that the required module is not an EventEmmiter instance. Therefore, it does not have an 'on' method.

Answer 2

Fundamental reason behind this bug should be something to do with the EventEmittter . Allow me to explain,

1. searcher.js inherits from EventEmitter (Line-26) Searcher.prototype = new process.EventEmitter ;

2. searcher-rediff.js , searcher-flipkart.js and searcher-landmarkonthenet.js extend from searcher.js , so they also inherit from EventEmitter .

3. 'on' method is actually defined in EventEmitter .

So, I think, for some reason, searcher.js is not able to inherit from EventEmitter and hence the method 'on' is missing.

Answer 3

You are trying to setup a listener on a module instead of an EventEmitter.

require('./searcher-rediff'); returns a Javascript module. I imagine there is actually an object in the searcher-rediff module that is the EventEmitter you are looking for.

Look through the searcher-rediff.js code to see where an EventEmitter is defined and exported, then you'll need to reference that.

In the end you'll probably end up with something like...

 var rediff = require('./searcher-rediff').searcher;