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Bindings give workers access to external resources and configuration settings. For ES modules syntax, bindings are delivered via the env object. For service worker syntax, bindings appear as global variables.

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Structure

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name
Text
required
Name of the binding. Becomes the property name in env (ES modules) or the global variable name (service workers).

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Binding types

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Simple values

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text
Text
A string value.
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data
Data
An ArrayBuffer.
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json
Text
A value parsed from JSON.

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Service bindings

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service
ServiceDesignator
Binding to a named service (possibly another worker).
bindings = [
  (name = "BACKEND", service = "my-service")
]

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Durable Objects

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durableObjectNamespace
DurableObjectNamespaceDesignator
Binding to a Durable Object namespace.In the common case where this refers to a class in the same worker, you can specify just a string:
bindings = [
  (name = "COUNTER", durableObjectNamespace = "Counter")
]
  • className: Exported class name implementing the Durable Object
  • serviceName: Service name defining the class (optional, defaults to current worker)
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durableObjectClass
ServiceDesignator
A Durable Object class binding without an actual storage namespace. Used to implement facets.

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Storage services

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kvNamespace
ServiceDesignator
A KV namespace. Operations are converted to HTTP requests to the named service.
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r2Bucket
ServiceDesignator
An R2 bucket binding. Operations are converted to HTTP requests.
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r2Admin
ServiceDesignator
An R2 admin API binding.

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Queues and events

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queue
ServiceDesignator
A Queue binding. Operations are converted to HTTP requests to the named service.
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analyticsEngine
ServiceDesignator
Analytics Engine binding. Allows workers to store information through Analytics Engine Events.Requires --experimental flag.

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Database connections

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hyperdrive
group
Hyperdrive binding for Postgres database caching and pooling.
  • designator: ServiceDesignator
  • database: Database name
  • user: Username
  • password: Password
  • scheme: Connection scheme

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WebAssembly and crypto

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wasmModule
Data
A WebAssembly module. The binding is a WebAssembly.Module instance. Only supported in service worker syntax.Deprecated: Use ES modules syntax with WASM modules instead.
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cryptoKey
CryptoKey
A CryptoKey instance for use with the WebCrypto API.By setting extractable = false, you prevent the worker from accessing raw key material; the key can only be used in WebCrypto operations.Fields:
  • raw, hex, base64: Raw key material (for symmetric keys)
  • pkcs8: Private key in PEM-encoded PKCS#8 format
  • spki: Public key in PEM-encoded SPKI format
  • jwk: Key in JSON format
  • algorithm: Algorithm name or JSON object
  • extractable: Allow worker to export key material (default: false)
  • usages: List of permitted operations (encrypt, decrypt, sign, verify, deriveKey, deriveBits, wrapKey, unwrapKey)

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Advanced bindings

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wrapped
WrappedBinding
Wraps a collection of inner bindings with common API functionality.
  • moduleName: Internal wrapper module name
  • entrypoint: Function name to call (default: “default”)
  • innerBindings: List of bindings passed to wrapper function
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fromEnvironment
Text
Takes the value from a system environment variable. The binding value is null if the environment variable is not set.
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unsafeEval
Void
Enables access to the UnsafeEval API.
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memoryCache
group
In-memory cache binding. Multiple isolates can access the same cache within the same process.
  • id: Cache identifier
  • limits: MemoryCacheLimits
    • maxKeys: Maximum number of keys
    • maxValueSize: Maximum size of a single value
    • maxTotalValueSize: Maximum total size of all values
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workerLoader
group
Dynamically load workers from code at runtime. Acts as a cache, automatically unloading unused workers.
  • id: Optional identifier for sharing across multiple bindings
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workerdDebugPort
Void
Provides a connect() method to dynamically connect to any workerd instance’s debug port via WorkerdDebugPort RPC interface.For local development and testing only.

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Parameter bindings

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parameter
group
Indicates the worker requires a binding of the given type, but it won’t be specified here. Another worker can inherit this worker and fill in the binding.
  • type: Expected type of this parameter
  • optional: If true, derived workers need not specify it (default: false)

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Example

bindings = [
  ( name = "API_KEY",
    text = "secret-key-value"
  ),
  ( name = "CONFIG",
    json = "{\"timeout\": 30}"
  ),
  ( name = "BACKEND",
    service = "backend-service"
  ),
  ( name = "COUNTER",
    durableObjectNamespace = "Counter"
  ),
  ( name = "KV",
    kvNamespace = "kv-service"
  ),
  ( name = "SECRET_KEY",
    cryptoKey = (
      raw = embed "secret.key",
      algorithm = (name = "AES-GCM"),
      extractable = false,
      usages = ["encrypt", "decrypt"]
    )
  )
]

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