Increment a Counter Field

Immutable Stateeasy

Course · Section 9: Data Structures, Modern Operators and Strings · Lecture 111: The Spread Operator (...)

Implement `incrementField(state, key)` returning a new object with the number at `key` increased by one.

Input: incrementField({"count":0}, "count")

Output: {"count":1}

Input: incrementField({"n":5}, "n")

Output: {"n":6}

+ 1 hidden test run on Submit.

Common pitfalls

state[key]++ mutates the object.
Calling the updater with a stale value when several increments happen in one render (prefer the functional updater in real React).

Approach & explanation (try first)

Return a new object with the counter field increased by one, leaving the rest of state intact.

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Run your code to see results.