Spies and carrying over Function Properties

[Jasmine Hegman]

Hey there, I have an interesting issue I discovered recently using a technique that I don't see used too often.

Essentially, because functions in JS are also first class objects, they can given properties. I wrote a component which uses this to hold its default options, and was surprised when it broke during a test. I could have made the spy not call through, but in this particular case I wanted it to. Inside the code, it tried to reference a function which was now spied, and the property did not exist, giving an error.

My fix was to store the default options object in a local variable in the test before spying, and then re-adding it to the function (now a spy wrapping function) after. This worked fine.

Anyway, I was just thinking and it may (or may not) be desirable to have a way to cause a spy to iterate over the function its going to spy on's properties and copy them over to make cases like this easier. I could see it being a performance hit, so maybe it should be a flag that can be passed to the spy functions?

Just food for though! Here's a really contrived example, but should illustrate the issue (I know it will look like there's better ways to do it, esp. with the fake object, its just simplified for illustration):

    it('wobbles', function() {

        // Pretend this source code to be tested

        var someObj = {

            someFunc: function() {

                return this.someFunc.stuff;

            }

        };

        someObj.someFunc.stuff = 'wheee';

        // Pretend this is the spec

        expect( someObj.someFunc() ).toBe('wheee'); // This will pass

        var stuffTemp = someObj.someFunc.stuff;

        spyOn(someObj, 'someFunc' ).andCallThrough();

        // someObj.someFunc.stuff = stuffTemp; // Try uncommenting this line and see the difference

        expect( someObj.someFunc() ).toBe('wheee'); // This will fail unless previous line is uncommented

        expect( someObj.someFunc ).toHaveBeenCalled(); // This will pass

    });

So yeah, this may not be a good enough of a use case to justify handling it, but I thought I'd bring it up since it is perfectly valid JavaScript (even if the inner function has to be tightly coupled with its function name since they took away arguments.callee)

[Davis W. Frank]

We're definitely going to make spies less intrusive in 2.0. We've not gotten to the code yet. 

But thanks for this feedback - this will help our design.

Thanks for using Jasmine and helping us make it better.

--dwf

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thx,

--dwf