为什么会出现错误：“ .isValid（）”不是一个函数？

Question

I am trying to validate a model called Book based on the availability of an attribute, with the help of this video . I am trying to follow the instructions on how to validate a Backbone.js model, but when I go to validate an instance of it called myBook using the .isValid() method, it returns the error:

Uncaught TypeError: myBook.isValid() is not a function

Here is my code:

<script src="https://ajax.cdnjs.com/ajax/libs/backbone.js/0.3.3/backbone-min.js"></script>
<script src="https://ajax.cdnjs.com/ajax/libs/underscore.js/1.1.4/underscore-min.js"></script>
<script language="Javascript">
  var Book = Backbone.Model.extend({
    validate: function(attrs) {
      if (!attrs.title) {
        return "What's a book without a title?!";
      }
    }
  });

  var myBook = new Book();
  /* validation is run in browser */
</script>

This was similar to what was in the video linked above. When I go into the console and run the .isValid() method, it returns said error.

Answer 1

It would have been hard to help you if you hadn't provided the code sample which has the answer in it.

Backbone 0.3.3 doesn't have isValid yet.

It was added in Backbone 0.9.1 but got removed in 0.9.9 .

It was improved and added back in 1.0 .

After upgrading Backbone and related to the comment about h.has is not a function , you also need to upgrade underscore.js as _.has was added in 1.3.1.

You should really use the latest stable release of the libs for your project as you'll avoid incompatibilities like that.