The JSON.stringify() method converts a JavaScript object to a JSON string. According to the JSON standard, functions are not a supported data type. Therefore, when the user object is stringified, the fullName property, which holds a function, is omitted from the resulting JSON string.

The JSON.parse() method then creates a new object, copiedUser, from this string. This new object will only contain the firstName and lastName properties. The subsequent line attempts to call copiedUser.fullName(), but since this property does not exist on copiedUser, its value is undefined. Attempting to invoke undefined as a function throws a TypeError.

A. Hello John Doe

This is incorrect because the fullName function is lost during the JSON.stringify process and does not exist on the copiedUser object, preventing a successful call.

B. Hello Dan

This is incorrect as the name "Dan" is not present in the code, and more importantly, the code fails with an error before it can produce any output.

C. Hello Dan Doe

This is incorrect for the same reasons as option B; the name is not in the code, and the execution halts due to a TypeError.

D. SyntaxError: Unexpected token in JSON

This is incorrect because the error is a TypeError, not a SyntaxError. A SyntaxError would occur if JSON.parse() received a malformed JSON string, but JSON.stringify() produces valid JSON.

1. MDN Web Docs (Mozilla): The JSON.stringify() documentation explicitly states its behavior with unsupported types.

Source: MDN Web Docs, JSON.stringify() method.

Reference: Under the "Description" section, it notes: "undefined, Function, and Symbol values are not valid JSON values. ...if any such values are encountered during conversion they are either omitted (when found in an object)..." This confirms the fullName property will be removed.

2. ECMAScript® 2023 Language Specification (ECMA-262, 14th edition): The official standard for JavaScript defines this behavior.

Source: ECMA-262, 14th Edition, June 2023.

Reference: Section 25.5.2, JSON.stringify ( value [ , replacer [ , space ] ] ). The internal abstract operation SerializeJSONProperty dictates that if the value of a property is a function, undefined, or a symbol, it returns undefined, which causes the property to be excluded from the final JSON object string.