Objects Are Passed by Reference

Behind the Scenesmedium

Course · Section 8: How JavaScript Works Behind the Scenes · Lecture 104: Object References in Practice (Shallow vs. Deep Copies)

Implement `addAge(person, age)` that sets the `age` property on the passed object and returns it. Objects are shared by reference.

Input: addAge({"name":"A"}, 30)

Output: {"name":"A","age":30}

Input: addAge({"name":"B","age":1}, 2)

Output: {"name":"B","age":2}

+ 1 hidden test run on Submit.

Common pitfalls

In React state you must NOT mutate like this; here it demonstrates reference semantics.

Approach & explanation (try first)

Because objects are passed by reference, assigning a property changes the caller's object.

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