How to check if a collection exists in Mongodb native nodejs driver?

The collectionNames method of the native driver's Db object accepts an optional collection name filter as a first parameter to let you check the existence of a collection:

db.collectionNames(collName, function(err, names) {
    console.log('Exists: ', names.length > 0);
});

In the 2.x version of the MongoDB native driver, collectionNames has been replaced by listCollections which accepts a filter and returns a cursor so you would do this as:

db.listCollections({name: collName})
    .next(function(err, collinfo) {
        if (collinfo) {
            // The collection exists
        }
    });

Using mongo-native driver and Node.js 7.6+, I use the following:

const collections = await db.collections();
if (!collections.map(c => c.s.name).includes(collName)) {
    await db.createCollection(collName);
}

EDIT

As @MattCochrane mentions, collection.s.name is no longer available; as @JohnnyHK and @weekens point out, the correct way is to use the listCollections() method:

const client = new MongoClient(connectionString, { useUnifiedTopology: true });
await client.connect();
const collections = await client.db().listCollections().toArray();
const collectionNames = collections.map(c => c.name);

listCollection() takes an optional filter.

Since MongoDB 3.0 you can simply run:

db.getCollectionNames()

which returns an array with the names of all the collections on current database:

[ "employees", "products", "mylogs"]

check Mongo DB Documentation, or you could also use db.getCollectionInfos() if you need more info about each collection

There is now a listCollections method in Node.js native driver. It returns information on all collections in current database. You can use it to check if a given collection is there:

collectionExists = function(name, cb) {
  mongoDb.listCollections().toArray(function(err, collections) {
    if (err) return cb(err);

    cb(null, collections.some(function(coll) {
      return coll.name == name;
    }));
  });
}

If you use mongodb 3.1.10. This is how to check if collections exist.

MongoClient.connect(url, { useNewUrlParser: true }, function(err, client) {
  if (err) throw err;

  var dbo = client.db("dbname");
  dbo.listCollections().toArray(function(err, items){
    if (err) throw err;

    console.log(items); 
    if (items.length == 0)
        console.log("No collections in database")  
  }); 
});

An updated answer which works with 3.6.* releases.

/**
 * Checks if a collection exists in a mongo database.
 * 
 * @param db a mongo db object.  eg.
 *    client = await MongoClient.connect(uri);
 *    db = client.db();
 * @param collectionName the name of the collection to search for
 * @returns {Promise<boolean>}
 */
async function doesCollectionExistInDb(db, collectionName) {
  const collections = await db.collections();
  return collections.some(
      (collection) => collection.collectionName === collectionName
  );
}

...

if (await doesCollectionExistInDb(db, 'products')) {
   // Do something, such as create a new collection
}

The collection.collectionName is part of the documented collection api as can be found here: http://mongodb.github.io/node-mongodb-native/3.6/api/Collection.html#collectionName

For nodejs with mongodb library (v 3.6.3) that's the only way I got it working:

const collectionName = 'products'
const exists = (await (await db.listCollections().toArray()).findIndex((item) => item.name === collectionName) !== -1)
console.log(exists)

Hope that helps others

actually, this works for me

  await db.createCollection(name, function (err, res) {
    if (err) {
        //console.log(err);
        if (err.codeName =="NamespaceExists") {
            console.log("Already Exists Collection  : " + name + "");
            return;
        }
    }
    console.log("Collection created! : "+name+"");

});

An async TypeScript function:

/**
 * Predicate function that checks if a collection exists in a given MongoDB database
 *
 * @param {Db} db Mongo database instance
 * @param {string} collectionName Name of collection
 *
 * @returns {boolean} true if collection exists, false otherwise
 */
export const doesCollectionExist = async (db: Db, collectionName: string): Promise<boolean> => {
  const cursor = db.listCollections({ name: collectionName })
  const result = await cursor.hasNext()
  await cursor.close()

  return result
}

The question refers to the native driver, but I got here searching how to do this in pymongo. Usually pymongo's api is identical to the JS api, but in this case collection_names doesn't have an argument for the collection's name (as in JohnnyHK's answer), but rather the first argument is a boolean (whether to include system collections). Since a string evaluates to True, this can be confusing. So I hope this helps future readers:

import pymongo

cl = pymongo.MongoClient()
db = cl['my-db']
if 'my-col' in db.collection_names(False):
   ...

/* set database */
let db          = client.db( 'crud' )

/* set collection */
let collection  = db.collection( 'categories' )

/* set query */
collection.find( {} ).toArray( ( err, result ) => {

if ( result.length > 0 )
{
    console.log("Exist");
}
else
{
    console.log("Not Exist");

    // create collection
}

}