TestMongoose.hx

import js.npm.mongoose.Model;
import js.npm.mongoose.Schema;
import js.npm.Mongoose;

class TestMongoose {
  public static function main(){
    
    Mongoose._.connect( 'mongodb://localhost/test' , cast start );
    
  }
  static function start(err){
    
    if( err != null ){
      trace(err);
      return;
    }
    
    var schema = new Schema({
      title : String,
      content : String,
      date : Date
    });
    
    var model : Models<Dynamic> = Mongoose._.model('Article',schema);
    
    // créer un article
    model.create({ title : 'My New Article', content : 'Bla bla'}, function(err, article){
      if( err == null || article == null ){
        throw "Error saving article...";
      }
      
      // mise à jour de l'article
      article.date = Date.now();
      article.save();
    });
    
  } 
  
}

I've updated the example with code to connect to a local mongo instance.

Also, regarding Haxe typing (to address your error with Null<js.npm.mongoose.Model<js.npm.mongoose.Schema>> has no field date)
... I just commited a change so Document (and thus Model) implements Dynamic
This should remove the error, and makes sense until we find a proper way to type Documents / Schemas / Models ...