JSON.stringify(): which values are not retained as expected

Useful to know

JSON.stringify() converts an appropriate JavaScript value into JSON text. In case of a property with value undefined, the field can be omitted : JSON.stringify({a: 1, b: undefined}) gives '{"a":1}'. In an array, undefined is represented as null. [1]

Therefore serialization is not a universal deep copy of an arbitrary state. Functions, cyclical connections, and other types have limitations. Before recording, define a scheme with the admissible data and check the losses. The text that appears valid JSON, may not yet contain all the properties that the application expected.