GlobalValue overview
The GlobalValue
module ensures that a single instance of a value is created globally, even when modules are imported multiple times (e.g., due to mixing CommonJS and ESM builds) or during hot-reloading in development environments like Next.js or Remix.
It achieves this by using a versioned global store, identified by a unique Symbol
tied to the current version of the effect
library. The store holds values that are keyed by an identifier, allowing the reuse of previously computed instances across imports or reloads.
This pattern is particularly useful in scenarios where frequent reloading can cause services or single-instance objects to be recreated unnecessarily, such as in development environments with hot-reloading.
Added in v2.0.0
Table of contents
utils
globalValue
Retrieves or computes a global value associated with the given id
. If the value for this id
has already been computed, it will be returned from the global store. If it does not exist yet, the provided compute
function will be executed to compute the value, store it, and then return it.
This ensures that even in cases where the module is imported multiple times (e.g., in mixed environments like CommonJS and ESM, or during hot-reloading in development), the value is computed only once and reused thereafter.
Signature
export declare const globalValue: <A>(id: unknown, compute: () => A) => A
Example
import { globalValue } from "effect/GlobalValue"
// This cache will persist as long as the module is running,
// even if reloaded or imported elsewhere
const myCache = globalValue(Symbol.for("myCache"), () => new WeakMap<object, number>())
Added in v2.0.0