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

Document Tags and Contributors

 Last updated by: kevin-albert,