While ES6 defines how to parse, link and execute a module, ES6 does not define when this parsing/linking/execution occurs. An additional extension to the HTML spec is required to say when a script is parsed as a module instead of normal global code. This work is ongoing.
Currently, the following entry points for modules are being considered:
an overload to the Worker constructor;
an overload to the importScripts Worker API;
Additionally, an ES6 module can recursively import other modules via import statements.
Any non-builtin imports from within a WebAssembly module would be treated as if they were import statements of an ES6 module. If an ES6 module imported a WebAssembly module, the WebAssembly module's exports would be linked as if they were the exports of an ES6 module. Once parsing and linking phases were complete, a WebAssembly module would have its start function, defined by the start module option, called in place of executing the ES6 module top-level script. By default, multiple loads of the same module URL (in the same realm) reuse the same instance. It may be worthwhile in the future to consider extensions to allow applications to load/compile/link a module once and instantiate multiple times (each with a separate linear memory).
This integration strategy should allow WebAssembly modules to be fairly interchangeable with ES6 modules (ignoring GC/Web API 🦄 future feature signature restrictions of the WebAssembly MVP) and thus it should be natural to compose a single application from both kinds of code. This goal motivates the semantic design of giving each WebAssembly module its own disjoint linear memory. Otherwise, if all modules shared a single linear memory (all modules with the same realm? origin? window?—even the scope of "all" is a nuanced question), a single app using multiple independent libraries would have to hope that all the WebAssembly modules transitively used by those libraries "played well" together (e.g., explicitly shared malloc and coordinated global address ranges). Instead, the dynamic linking future feature is intended to allow explicitly sharing state between module instances.
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I'm interested in helping with this, although perhaps not quite championing.