Insert at Index

Immutable Arraysmedium

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

Implement `insertAt(list, index, item)` returning a new array with `item` inserted at `index`.

Sample tests

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

Output: [1,9,2,3]

Input: insertAt([], 0, 5)

Output: [5]

+ 1 hidden test run on Submit.

Hints

Common pitfalls

splice inserts in place and mutates the original array.
Forgetting that an index beyond the length just appends the item.

Learning resources

React: Updating Arrays in State

Approach & explanation (try first)

slice(0, index) is everything before the insertion point and slice(index) is everything after. Spreading them around the new item produces a fresh array with the item inserted, leaving the original alone.

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