Question

var Model = function(client, collection) {
  this.client = client;
  this.collection = collection;
};

Model.prototype = {
  constructor: Model,
  getClient: function(callback) {
    this.client.open(callback);
  },
  getCollection: function(callback) {
    var self = this;

    this.getClient(function(error, client) {
      client.collection(self.collection, callback);
    });
  },
  extend: function(key, fn) {
    var self = this;

    this[key] = function() {
      fn.call(self); // A
    };
  }
};

What I want to achieve is that I can “extend” the functionality of the model.

var userModel = new Model(client, 'users');
userModel.extend('create', function(data, callback) {
  this.getCollection(function(error, collection) {
    collection.insert(data, { safe: true }, function(error, doc) {
      callback.call(doc);
    });
  });
});

userModel.create({ fullName: 'Thomas Anderson' }, function() {
  console.log(this); // { _id: '123456789012345678901234', fullName: 'Thomas Anderson' }
});

Someway at A, I have to do parameter passing, the parameter count of the custom “create” function (data and callback) are variable.

Is this possible and if so how?

Answer 1

Yep! You want to use the .apply method over the .call method. Both apply context, but the .apply method takes an array for arguments–or an arguments collection itself!

extend: function(key, fn) {
    var self = this;

    this[key] = function() {
      fn.apply(self,arguments); // the special arguments variable is array-like
    };
  }