Durable State

One fundamental feature that separates Membrane from other serverless runtimes is that it is stateful.

You don’t need to store data in a database or file to persist it—instead, the state of your program (the entire JS heap) is transparently and efficiently persisted every time it changes.

Managing state

Programs have a state object that persists state between updates (i.e. deploying your program on save) and invocations (i.e. running your program manually or on a timer). To keep data around, put it in the state object, and that’s it.

import { const state: anyThis object is automatically persisted by Membrane.
Its type is defined by the exported State interface
below.state } from "membrane";

const state: anyThis object is automatically persisted by Membrane.
Its type is defined by the exported State interface
below.state.count ??= 0;

export function function count(): voidcount() {
  const state: anyThis object is automatically persisted by Membrane.
Its type is defined by the exported State interface
below.state.count++;
}

You can also provide type information for state by exporting a State type or interface. The membrane module imports this type/interface to add type information to state.

export interface State {
  State.count: numbercount: number;
}

JavaScript objects as the database

Durability means you can treat your JavaScript objects as a database. So you can store state in one call to a Membrane program and use it again in a subsequent call.

This persistence model enables behavior that wouldn’t be possible in most serverless runtimes. For example, Promises can be await’ed indefinitely without worrying about execution timeouts. You might use an indefinite await to wait for an email handler.