The structured clone algorithm

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The structured clone algorithm copies complex JavaScript objects. It is used internally when invoking {{DOMxRef("WorkerGlobalScope.structuredClone", "structuredClone()")}} , to transfer data between Workers via {{domxref("Worker.postMessage()", "postMessage()")}} , storing objects with IndexedDB, or copying objects for other APIs.

It clones by recursing through the input object while maintaining a map of previously visited references, to avoid infinitely traversing cycles.

Things that don’t work with structured clone

• {{jsxref("Function")}}  objects cannot be duplicated by the structured clone algorithm; attempting to throws a DataCloneError exception.
• Cloning DOM nodes likewise throws a DataCloneError exception.
• Certain object properties are not preserved:
  • The lastIndex property of {{jsxref("RegExp")}}  objects is not preserved.
  • Property descriptors, setters, getters, and similar metadata-like features are not duplicated. For example, if an object is marked readonly with a property descriptor, it will be read/write in the duplicate, since that’s the default.
  • The prototype chain is not walked or duplicated.
  • Class private elements are not duplicated. (Although internal fields of built-in types may.)

Supported types

JavaScript types

• {{jsxref("Array")}} 
• {{jsxref("ArrayBuffer")}} 
• {{jsxref("Boolean")}} 
• {{jsxref("DataView")}} 
• {{jsxref("Date")}} 
• {{jsxref("Error")}}  types (but see Error types below).
• {{jsxref("Map")}} 
• {{jsxref("Number")}} 
• {{jsxref("Object")}}  objects: but only plain objects (e.g., from object literals).
• Primitive types, except symbol.
• {{jsxref("RegExp")}} : but note that lastIndex is not preserved.
• {{jsxref("Set")}} 
• {{jsxref("String")}} 
• {{jsxref("TypedArray")}} 

Error types

For Error types, the error name must be one of: {{jsxref("Error")}} , {{JSxRef("EvalError")}} , {{JSxRef("RangeError")}} , {{JSxRef("ReferenceError")}} , {{JSxRef("SyntaxError")}} , {{JSxRef("TypeError")}} , {{JSxRef("URIError")}}  (or will be set to “Error”).

Browsers must serialize the properties name and message, and are expected to serialize other “interesting” properties of the errors such as stack, cause, etc.

{{JSxRef("AggregateError")}}  support is expected to be added to the specification in whatwg/html#5749 (and is already supported in some browsers).

Web/API types

• {{domxref("AudioData")}} 
• {{domxref("Blob")}} 
• {{domxref("CropTarget")}} 
• {{domxref("CryptoKey")}} 
• {{domxref("DOMException")}} : browsers must serialize the properties {{domxref("DOMException.name","name")}}  and {{domxref("DOMException.message","message")}} . Other attributes may also be serialized/cloned.
• {{domxref("DOMMatrix")}} 
• {{domxref("DOMMatrixReadOnly")}} 
• {{domxref("DOMPoint")}} 
• {{domxref("DOMPointReadOnly")}} 
• {{domxref("DOMQuad")}} 
• {{domxref("DOMRect")}} 
• {{domxref("DOMRectReadOnly")}} 
• {{domxref("EncodedAudioChunk")}} 
• {{domxref("EncodedVideoChunk")}} 
• {{domxref("FencedFrameConfig")}} 
• {{domxref("File")}} 
• {{domxref("FileList")}} 
• {{domxref("FileSystemDirectoryHandle")}} 
• {{domxref("FileSystemFileHandle")}} 
• {{domxref("FileSystemHandle")}} 
• {{domxref("GPUCompilationInfo")}} 
• {{domxref("GPUCompilationMessage")}} 
• {{domxref("GPUPipelineError")}} 
• {{domxref("ImageBitmap")}} 
• {{domxref("ImageData")}} 
• {{domxref("RTCCertificate")}} 
• {{domxref("RTCEncodedAudioFrame")}} 
• {{domxref("RTCEncodedVideoFrame")}} 
• {{domxref("VideoFrame")}} 
• {{domxref("WebTransportError")}} 

[!NOTE] Serializable objects are marked up in Web IDL files with the attribute [Serializable].

See also

• HTML Specification: Safe passing of structured data
• Transferable objects
• {{DOMxRef("Window.structuredClone()")}} 
• {{DOMxRef("WorkerGlobalScope.structuredClone()")}} 
• {{domxref("window.postMessage()")}} 
• Web Workers
• IndexedDB