Re: Object.equals() and Object.clone()

[Alexander Jones]

Object has this unfortunate complication of prototypes, i.e.:

```
const objA = {foo: 1, bar: 2};
const objB = Object.create(objA);
equals(objA, objB) === ?
```

And also there is metadata on each property that can vary (one object has a
property which is configurable, and the other has the same property which
is not configurable), and raise similar questions.

Neither of these questions exist on ES's Map type, or Immutable.js's Map
and List types, for example.

IMO we should be looking at ways to make those types more suitable for many
of the use cases of Object.

On 15 November 2016 at 01:25, Kevin Barabash  wrote:

> It would be nice if deep equality checking and deep cloning of objects was
> included in the standard library.  Has there been any proposals around
> including these in the past?
>
> – Kevin
>
>
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Re: Proposal: Symbol.templateTag

[Alexander Jones]

As promised (to myself!) I've written a stage-0.

https://github.com/alex-weej/es-symbol-template-tag

Your feedback is greatly appreciated.

Thanks

On 18 November 2016 at 00:30, Alexander Jones  wrote:

> OK, I was thinking about this incorrectly and I think you're right - it
> doesn't Break The Web. It's exactly the same as when @@isConcatSpreadable
> and @@toStringTag were introduced, as far as I can tell.
>
> If no-one has any obvious objections to save me the effort, I'll try to
> write up a stage 0 this weekend.
>
> Thanks
>
>
>
> On 17 November 2016 at 04:58, Mark S. Miller  wrote:
>
>> Hi Alexander, I have run into this myself. It is a real problem, and I
>> like the nature of your proposed solution. But I don't understand how it
>> might break the web. If Symbol.templateTag is a new symbol, guaranteed
>> unequal to any prior value, how can introducing it, and new behavior
>> conditional on it, change any existing behavior?
>>
>>
>>
>>
>> On Wed, Nov 16, 2016 at 5:02 PM, Alexander Jones  wrote:
>>
>>> Hi es-discuss!
>>>
>>> Template tags are a great feature with many novel applications, IMO
>>> approaching macro-level expressiveness. But due to their nature in this
>>> context, it's helpful if tags are named quite tersely. Unfortunately, if
>>> you have existing API, this can be challenging.
>>>
>>> Let's say I have a DSL (domain-specific language), and I *may*,
>>> unsafely, generate typed snippets of code containing that DSL like so:
>>>
>>> ```js
>>> function dsl(code: string) {
>>> // `code` MUST be well-formed
>>> }
>>>
>>> const someStatement = dsl("val foo = " + dslEncode(foo));
>>> ```
>>>
>>> Let's say I'd like to add support in my library for ES6 clients such
>>> that they can do:
>>>
>>> ```js
>>> const someStatement = dsl`val foo = ${foo}`;
>>> ```
>>>
>>> where the `dsl` template tag would be implemented such that `dslEncode`
>>> is used on each interpolated expression.
>>>
>>> Unfortunately, the `dsl` function's arguments are already defined and
>>> can't be changed. I'd need a new name, like `dsl.tag`, which would end up
>>> being a fair bit more verbose.
>>>
>>> Would it be possible, at this point, to introduce a new behaviour into
>>> ES such that instead of merely calling the tag object, the implementation
>>> first checks for a `Symbol.templateTag` property on the tag object, and if
>>> it exists, it is invoked? I'd guess this can't Break The Web because no-one
>>> can realistically be using an existing function as a template tag if it was
>>> not already designed for it.
>>>
>>> ```js
>>> const someStatement = dsl`val foo = ${foo}`;
>>> // desugars to, approximately
>>> const someStatement = (dsl[Symbol.templateTag] || dsl)(["val foo =",
>>> ""], foo);
>>> ```
>>>
>>> To be honest, I am kind of surprised it wasn't already implemented like
>>> this, but maybe there were performance concerns with the branching.
>>> Interested in your thoughts.
>>>
>>> Thanks
>>>
>>> Alex
>>>
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>>
>>
>> --
>> Cheers,
>> --MarkM
>>
>
>
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