在JS中访问属性时如何抛出错误？

Question

I'd like to have an attribute throw an error if it's not defined, as in this question . Each of the answers to that question suggest using Python's @property decorator to raise an exception if the field isn't defined. How can I do that in JS?

EDIT:

I'm hoping for the equivalent of:

var MyObj = {
  method: function(){
    throw new Error('This method is not implemented');
  }
};

...but closer to:

var MyObj = {
  attribute: throw new Error('This attribute is not defined');
};

Answer 1

This question can be broken down into two parts,

var myObj = {}; // just an example, could be a prototype, etc

How can I add a non-enumerable property to an Object ?

This is done with Object.defineProperty

Object.defineProperty(myObj, 'foo', {get: function () {/* see next part */}});

I defined a getter , so you'll see the error message without needing to use () to invoke the function.

How can I throw an error?

This is as simple as using the throw statement. JavaScripts closest Error type to what you're looking for is most likely a ReferenceError .

throw new ReferenceError("Subclasses should implement this!");