The structured clone algorithm copies complex JavaScript objects. It is used internally when invoking structuredClone()
, to transfer data between Workers via 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.
-
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 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.