Effect

Effect (Effect-TS) is a TypeScript library for building programs where errors, dependencies and concurrency are tracked in the type system. Site: https://effect.website

Core idea

Effect<A, E, R> is a lazy description of a program:

• A: success value
• E: typed, expected errors
• R: required environment (services), provided later through Layers

Nothing runs until you hand the effect to a runtime. Effects are written with Effect.gen (generator syntax, similar to async/await) or with pipes.

What it bundles

• Typed errors (Either, Option, tagged errors, catchTag)
• Dependency injection (Context, Layer)
• Structured concurrency (fibers, interruption, Effect.all, Effect.race)
• Retries and scheduling (Schedule, Effect.retry, Effect.repeat)
• Resource safety (Scope, acquireRelease)
• Streams (Stream, Channel, Queue, PubSub)
• State and STM (Ref, STM)
• Schema validation and encoding (Schema)
• Observability (tracing, metrics, logging, OpenTelemetry integration)
• A standard library (Chunk, HashMap, Duration, DateTime, ...)

Tradeoffs

• Steep learning curve, large API surface, reads like Haskell/Scala (ZIO) in TypeScript.
• Everything is expressed through effects, so adoption tends to be all-in.

See also

• Effect in dotnet

Backlinks

• Effect in dotnet

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