Proposal: Stop using Object.freeze/Object.seal on most of our Javascript Objects

Joseph Hildebrand jhildebrand at mozilla.com
Mon Nov 20 19:09:39 UTC 2017


Tests seem like a reasonable place to take a perf trade off though, right?

Mobile/terse. DYAC. 

> On Nov 20, 2017, at 10:29 AM, Tom Schuster <tom at schuster.me> wrote:
> 
> Please don't use proxies unnecessarily. They are bad for performance. 
> 
>> On Mon, Nov 20, 2017 at 5:05 PM, Joe Hildebrand <jhildebrand at mozilla.com> wrote:
>> You could also potentially use a Proxy object:
>> 
>> https://gist.github.com/hildjj/1ac6e3d52e4e0d23f6289d73c1840a5a
>> 
>> > On Nov 20, 2017, at 9:00 AM, Richard Newman <rnewman at mozilla.com> wrote:
>> >
>> > Are there alternative ways we could achieve the same without the (or with low) complexity/overhead?
>> >
>> > If I'm understanding correctly what you're trying to do, the typical suggestion here is to not use global singletons. That way you don't need to dig into the guts of a globally visible object in order to test it; you can pass your own part-mocked Object instance into whatever mechanism is trying to call `Object.foo`.
>> >
>> > In your `foo`/`bar` case, you'd pass a `MockObject` to `bar`, and verify that `MockObject.foo` was called. We do this all the time in codebases that use less dynamic languages (e.g., Fennec and Firefox for iOS).
>> >
>> > This doesn't help you to test existing singleton-based JS code… but then, if that code is already using Object.freeze, then you already can't, and you'll be having to change _something_.
>> >
>> > I mostly agree with Nicolas's sentiment; poking at the guts of code outside your own module (or even in your own module!) isn't really a kind of software development that I feel we should encourage. If we find that gut-poking is the only good way to write tests for a component, then I would rather we revisit the design of the component instead of making it mutable. Refactoring for testability is A-OK in my book.
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>>>> Joe Hildebrand
>> 
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