JavaScript Snippet

Insert, Update, Remove Items by Index

Difficulty: Easy

Index-based mutations are where most array bugs come from: `splice` mutates in place and is easy to misuse, while `slice` plus spread gives you a copy without mutating the input. This snippet contrasts the mutable and immutable forms for the four common index operations (remove by index, update by index, insert at index, remove all matching a predicate). Keep mutation explicit at the call site so reviewers know whether the original array survives.