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Web Workers API: Structured clone algorithm

The structured clone algorithm is an algorithm defined by the HTML5 specification for copying complex JavaScript objects. It is used internally when transferring data to and from Workers via postMessage(). It builds up a clone by recursing through the input object while maintaining a map of previously visited references in order to avoid infinitely traversing cycles.

Things that don't work with structured clone

  • Error and Function objects cannot be duplicated by the structured clone algorithm; attempting to do so will throw a DATA_CLONE_ERR exception.
  • Attempting to clone DOM nodes will likewise throw a DATA_CLONE_ERR exception.
  • Certain parameters of objects are not preserved:
    • The lastIndex field of RegExp objects is not preserved.
    • Property descriptors, setters, and getters (as well as similar metadata-like features) are not duplicated. For example, if an object is marked read-only using a property descriptor, it will be read-write in the duplicate, since that's the default condition.
    • The prototype chain does not get walked and duplicated.

Supported types

Object type Notes
All primitive types However not symbols
Boolean object
String object
Date
RegExp The lastIndex field is not preserved.
Blob
File
FileList
ArrayBuffer
ArrayBufferView This basically means all typed arrays like Int32Array etc.
ImageData
Array
Object This just includes plain objects (e.g. from object literals)
Map
Set

See also

© 2005–2017 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm