The JavaScript Promise Integration specification is an in-progress specification intended to make it easier for applications written in Wasm to perform synchronous IO on non-blocking runtimes like the browser.

References

• WebAssembly/js-promise-integration (specification)
• Chrome blog: Introducing the WebAssembly JavaScript Promise Integration API
• Chrome blog: WebAssembly JSPI is going to origin trial
• Firefox JSPI specification position (positive)
• Firefox bugzilla tracking issue