Question

It is easy to bind to the ‘error’ event of an existing model, but what is the best way to determine if a new model is valid?

Car = Backbone.Model.extend({
  validate: function(attributes) {
    if(attributes.weight == null || attributes.weight <=0) {
      return 'Weight must be a non-negative integer';
    }
    return '';
  }
});

Cars = Backbone.Collection.extend({
  model: Car
});

var cars = new Cars();
cars.add({'weight': -5}); //Invalid model. How do I capture the error from the validate function?

Answer 1

Validation logic can be triggered explicitly by calling the validate method of your model. This will not, however, cause an error event to be triggered. You can trigger an error event manually for a model by calling the trigger method.

One way to achieve your desired behavior is to manually trigger the event in your initialization method:

Car = Backbone.Model.extend({
  initialize: function () {
    Backbone.Model.prototype.initialize.apply(this, arguments);
    var error = this.validate(this.attributes);
    if (error) {
      this.trigger('error', this, error);
    }
  },
  validate: function(attributes) {
    if(attributes.weight == null || attributes.weight <=0) {
      return 'Weight must be a non-negative integer';
    }
    return '';
  }
});