Update by Index

Immutable Arrayseasy

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

Implement `updateAt(list, index, value)` returning a new array with the element at `index` replaced by `value`.

Sample tests

Input: updateAt([1,2,3], 1, 9)

Output: [1,9,3]

Input: updateAt([5], 0, 7)

Output: [7]

+ 1 hidden test run on Submit.

Hints

Common pitfalls

list[index] = value mutates the original array.
When elements are objects, returning value replaces the whole object; spread it if you only mean to change one field.

Learning resources

React: Updating Arrays in State

Approach & explanation (try first)

map returns a new array. At the matching index you return value; at every other position you return the original element, so only one slot changes while the rest are preserved.

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