JSONResource.js

function JSONResource(obj) {
  this._watchFields = new Array();
  this._serverCopy = obj;
  
  for (var field in obj) {
    if (obj.hasOwnProperty(field)) {
      this._watchFields.push(field);
      this[field] =  obj[field];
    }
  }
}

module.exports = JSONResource;

JSONResourceCollection.js

var JSONResource = require('./JSONResource');

encodeObj = function(obj) {
  var str = [];
  for(var p in obj)
    if (obj.hasOwnProperty(p)) {
      str.push(encodeURIComponent(p) + "=" + encodeURIComponent(obj[p]));
    }
  return str.join("&");
}


function JSONResourceCollection(source, Type) {
    if (Type instanceof JSONResource) {
        this.Type = Type;
    } else {
        throw "The Type must be a inherit from JSONResource";
    }
    this.source = source;
    
    this._queryStr = new String();
    this.query = new Object();
    this._collection = new Array();
}

module.exports.JSONResourceColleciton;

usage.js

// This throws the "The Type must be a inherit from JSONResource" error

collection = new JSONResourceCollection("someurl", JSONResource);

Hmm, I'd look into what JSONResource thinks it is. Maybe a console.dir(JSONResource) on line 2?

function Foo() {}

function validateFoo(Type) {
  if (Type.prototype.isPrototypeOf(new Foo())) {
    return true;
  } else {
    throw new TypeError('Must be a Foo');
  }
}

console.log(validateFoo(Foo));