DO Transforms API

Definition and registration

defineTransform<TTarget, TContext>()

Starts a typed transform definition. Chain .caller(factory) and/or .callee(factory) to define its two boundaries.

registerTransform(transform, options?)

Binds callee options for use in applyTransforms. Parameterless transforms do not take an options argument.

applyTransforms(TargetClass, config)

Registers transforms on all async methods or selected methods:

applyTransforms(TargetClass, {
  all: [registerTransform(globalTransform, options)],
  methods: {
    write: [registerTransform(writeTransform, options)],
  },
});

Caller wrapping

.with(transform, options?)

The Vite plugin adds typed .with(...) access to configured Durable Object and service bindings.

createTransformStub(rawStub)

Manually wraps one RPC target when automatic Vite wrapping is not used.

withTransforms(namespace)

Manually wraps a Durable Object namespace so stubs returned from it support transforms.

Context

createTransformContextTarget(target, context)

Returns a pipelined RPC target carrying typed context. Expose it from setContext() when caller transforms call next({ context }).

TransformContextTarget

The underlying context-target class. Most integrations should use createTransformContextTarget instead of constructing it directly.

Vite

doTransforms(options?)

Import from @repo/do-transforms/vite. Reads Wrangler bindings, injects wrappers, and emits generated declarations.

doTransforms({ wrangler: './wrangler.jsonc' })

Place it before cloudflare() in the Vite plugin array.

Return-type behavior

Transform	Resulting async return type
betterResultCodec	Preserves or rehydrates Result<T, E>
errorBoundary	Result<T, unknown>
abortAsSuccess	Result<T | undefined, never>
timeout	Original method type
retry	Original method type
largeObjectStream	Original method type

Transform chains validate target compatibility, options, context compatibility, async method names, and transformed return types at compile time.