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What is the difference between slice and splice?

JavaScript Arrays Basic Fresher Coding 1 min read

Quick Answer

slice(start, end) returns a shallow copy of a portion of the array and doesn't change the original. splice(start, deleteCount, ...items) mutates the array — removing and/or inserting elements in place — and returns the removed elements.

The names are similar but one mutates and one doesn't. slice returns a copy of a chunk of the array and leaves the original alone. splice changes the array in place — you give it a start index, how many to remove, and optionally items to insert, and it returns whatever it removed. So in something like Redux where I need immutability, I use slice or spread, never splice. An easy mnemonic: splice has the extra letter and does the extra damage.

  • [1,2,3,4].slice(1,3) → [2,3]; original unchanged.
  • arr.splice(1, 2) → removes 2 elements from index 1, returns them, and shortens arr.
  • arr.splice(1, 0, 'x') → inserts 'x' at index 1, deletes nothing.
  • For immutable updates (React/Redux state) use slice, spread, filter, map — never splice.
  • Also String.prototype.slice exists; strings have no splice.
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