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ChallengeIntermediate9 min

Spot shared object mutation

Fix the output so copying an object does not mutate the original lesson state.

Update the copy logic so the first log prints `1` and the second log prints `2`. Do not change the final two `console.log` calls.

Challenge Brief

Solve the exercise by editing the starter code and running it in the panel. Compare your result against the expected outcome, then refine your solution until the behavior matches.

  1. 1. Read the prompt carefully and identify the missing behavior.
  2. 2. Update only the parts of the starter code needed to solve it.
  3. 3. Run the code and compare actual output with the expected result.

Hints

  • Assigning an object to another variable shares the same reference.
  • Create a shallow copy before changing `copied.completed`.
  • Spread syntax is enough for this object shape.

Related Concepts

Spread and Rest

Spread expands values outward, while rest collects remaining values into an array or object.

Pass by Value vs Reference Behavior

Primitives are copied by value, while objects and arrays behave through shared references.

Objects

Objects store related data and behavior as key-value pairs and are one of JavaScript’s core building blocks.

Challenge Workspace

reference-mutation.js

Edit the code, run it in the browser, and inspect the console output below. Reset restores the original snippet for this page.

Editor

7 lines

Output

0 entries

Mode

challenge

Workspace Notes

Changes stay local until you run the code. Reset restores the original snippet immediately for another pass.

Live editing

Safe to change before every run.

Fast reset

Return to the original starter instantly.

reference-mutation.js
7 linesMonaco Editor
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Editor Actions

Run your solution and compare the result with the expected challenge output.

Console0 entries

Run the code to see output here.

Challenge Result

Run the code to check whether your solution matches the expected outcome.

Expected Output

1
2

Continue in Playground

Open this starter code in the shared playground if you want a focused space for experimenting outside the challenge page.

Open in Playground