Ignore undefined fields in Collection.find()

[tkers]

I noticed when calling the find(selector, fields) method on a collection with fields set to undefined, I get a TypeError: Object.keys called on non-object. When checking out the problem, I found that the collection.js module checks if argument.length >= 2 which evaluates to true even if argument[1] is not explicitly set. I.e. the code is trying to use the fields argument as if it's set, throwing the error eventually.

Fixed it by comparing fields !== undefined instead of using the argument count.

In our application, we basically do something like this:

// fields is optional
function getRecords(arg1, arg2, fields) {
    // validate arg1, arg2 etc...

     // build the query with arg1, arg2
    var query = {};

    return collection.find(query, fields);
}

I changed fields to fields || {} as a quick work-around for now, but I'm pretty sure undefined should be just ignored in the module.

[christkv]

this is legacy behavior you should use. I support it as best as possible but the code is brittle so any changes like these breaks behavior that unfortunately people still relay on.

db.collection('data').find({}).project({a:1}).toArray()

[tkers]

I understand your point of view, although in this particular situation I have my doubts that developers could rely on this behaviour. You just wouldn't expect a function to try and parse a argument that is not really passed to it.

To be honest I'm not completely sure why JS also counts undefined values in arguments.length, maybe there is actually a good reason for this. But I think that for most use cases you shouldn't check if an optional parameter is passed or not in this way. Just as a future consideration then :)

Anyway, I wasn't aware that this is a legacy way of using the module. Will update my code accordingly. Thanks for the quick response!