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https://github.com/tc39/proposal-compartments

Compartmentalization of host behavior hooks for JS
https://github.com/tc39/proposal-compartments

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Compartmentalization of host behavior hooks for JS

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README 

        
# Compartments



**Stage**: 1



**Champions**:



* Mark S. Miller, Agoric

* Caridy Patiño, Salesforce

* Patrick Soquet, Moddable

* Kris Kowal, Agoric

* Jack Works, Sujitech

* Guy Bedford, OpenJS Foundation



**Emeritus**:



* Bradley Farias, GoDaddy

* Jean-Francois Paradis, Salesforce



# Synopsis



Compartments are a mechanism for isolating and providing limited power to

programs within a shared realm.

Each compartment shares the intrinsics of a realm, but a different set of

evaluators (`eval`, `Function`, and a new evaluator, `Module`) and a global

object.

Having a separate global object allows each compartment to be granted access to

only those powerful objects it needs, its own isolated evaluators, powerless

constructors, and shared prototypes.



The Compartments proposal was approved for Stage 1 (exploration of a problem)

with the charter, "to compartmentalize host behaviors".

The problem we set out to solve was excess authority flowing from global scope

and host behaviors into third-party dependencies and plugins in large

applications.

Through exploring this problem, we discovered that the bulk of the solution, by

weight, was virtualizing the EcmaScript module loader.

Provided an EcmaScript module loader, we could then build a solution for

isolating code for both scripts and modules.



Over the course of two years, we refined the Compartment class to account for

the need to make and import bundles, emulate various host module specifier

namespaces, link modules between multiple compartments, and support

non-EcmaScript module languages.



We then began working with champions of module blocks, module fragments,

deferred import, and import reflection to ensure these proposals were coherent.

From these discussions, we discovered a set of lower-level interfaces from

which compartments could be constructed in user code that were more coherent

with these other proposals.



With that, the Compartments proposal consists of five layers:



- [Module and ModuleSource][0]: Provide first-class `Module` and

  `ModuleSource` constructors and extend dynamic import to operate on `Module`

  instances. ([Specification Changes][0-spec])



- [Surface Module Source Static Analysis][1]: Extend instances of

  `ModuleSource` such that they reflect certain results of static analysis,

  like their `import` and `export` bindings, such that tools can inspect module

  graphs.



- [Virtual Module Sources][2]: Extend the `Module` constructor such that it

  accepts virtual module sources: objects that implement a protocol that is

  sufficient for virtualizing the evaluation of modules in languages not

  anticipated by ECMA-262 or host implementations.



- [Evaluators][3]: Provide an `Evaluators` constructor that produces

  a new `eval` function, `Function` constructor, and `Module` constructor

  such that execution contexts generated from these evaluators refer

  back to this set of evaluators, with a given global object and virtualized

  host behavior for dynamic import in script contexts.



- [Compartment][4]: Compartments are a high-level mechanism for isolating

  and providing limited power to programs within a shared realm.

  Compartments can be implemented in user code using `Evaluators`, `Module`,

  and `ModuleSource`.



[Motivating use cases for module proposal features](./GRAPH.md) illustrates

the motivation for each feature from the layers of this Compartments proposal

and related module proposals.



[0]: ./0-module-and-module-source.md

[0-spec]: https://tc39.es/proposal-compartments/0-module-and-module-source.html

[1]: ./1-static-analysis.md

[2]: ./2-virtual-module-source.md

[3]: ./3-evaluator.md

[4]: ./4-compartment.md