meteor/meteor · error · Error

A "url" property or function must be specified

Error message

A "url" property or function must be specified

What it means

Backbone's urlError() helper throws when a model or collection needs a URL to sync (save/fetch/destroy) but neither the instance nor its class defines a `url` property or `url` function, and no urlRoot/collection url was inferable. Backbone cannot perform a server sync without knowing the endpoint. Backbone is a vendored, deprecated Meteor package.

Source

Thrown at packages/deprecated/backbone/backbone.js:1436

    // Correctly set child's `prototype.constructor`.
    child.prototype.constructor = child;

    // Set a convenience property in case the parent's prototype is needed later.
    child.__super__ = parent.prototype;

    return child;
  };

  // Helper function to get a value from a Backbone object as a property
  // or as a function.
  var getValue = function(object, prop) {
    if (!(object && object[prop])) return null;
    return _.isFunction(object[prop]) ? object[prop]() : object[prop];
  };

  // Throw an error when a URL is needed, and none is supplied.
  var urlError = function() {
    throw new Error('A "url" property or function must be specified');
  };

}).call(this);

View on GitHub (pinned to 5076d2f818)

Solutions

1. Define urlRoot on the model class (e.g. urlRoot: '/api/items') or url on the collection class.
2. Attach the model to a collection that has a url before calling save/fetch.
3. Pass {url: '/api/items'} in the options of the specific sync call.

Example fix

// before
const Item = Backbone.Model.extend({});
const item = new Item({ name: 'x' });
item.save(); // throws: no url

// after
const Item = Backbone.Model.extend({ urlRoot: '/api/items' });
const item = new Item({ name: 'x' });
item.save();

function ensureUrl(modelOrCollection) {
  const hasUrl = Boolean(
    modelOrCollection.url ||
    (modelOrCollection.collection && modelOrCollection.collection.url) ||
    modelOrCollection.urlRoot
  );
  if (!hasUrl) throw new Error('Model/Collection needs a url or urlRoot before sync');
}

function hasUrl(target) {
  return Boolean(target.url || target.urlRoot || (target.collection && target.collection.url));
}

When it happens

Trigger: model.save() on a model with no url and no collection with a url; collection.fetch() on a collection with no url property; calling sync methods before wiring the model to a collection that provides the url.

Common situations: Defining a model class without urlRoot; instantiating a model outside any collection and calling save; forgetting to set url on a collection subclass.

Related errors

• Can't add an invalid model to a collection
• Cannot sort a set without a comparator
• Backbone.history has already been started
• Backbone.History is client-only, can't start on the server
• Method "${events[key]}" does not exist

AI-assisted analysis of meteor/meteor@5076d2f818 (2026-08-13). Data as JSON: /api/errors/52e68abd436618d8. Report an issue: GitHub.