The structured clone algorithm

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.

Things that don't work with structured clone

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.

Note: Native Error types can be cloned in Chrome, and Firefox is working on it.

Supported types

Object type	Notes
All primitive types	However, not symbols.
`Boolean` objects
`String` objects
`Date`
`RegExp`	`lastIndex` is not preserved.
`Blob`
`File`
`FileList`
`ArrayBuffer`
`ArrayBufferView`	Including other typed arrays.
`ImageBitmap`
`ImageData`
`Array`
`Object`	Only plain objects (e.g. from object literals)
`Map`
`Set`

The structured clone algorithm

Things that don't work with structured clone

Supported types

See also