slice = copy
slice returns a shallow copy of a portion of the array.
It does not modify the original array.
JavaScript Tutorial
JavaScript slice() and splice()
slice copies part of an array without changing it, while splice edits the array in place.
Knowing the difference prevents mutation bugs.
Why We Need It
Many bugs come from unintentional array mutation.
Choosing the right method keeps your data flow predictable.
Syntax
array.slice(start, end)
array.splice(start, deleteCount, ...items)Basic Example
1. slice
const items = ["a", "b", "c", "d"];
const part = items.slice(1, 3);
console.log(part); // ["b", "c"]
console.log(items); // unchangedslice copies without mutation.
Real World Example
2. splice remove
const items = ["a", "b", "c", "d"];
items.splice(1, 2);
console.log(items); // ["a", "d"]splice removes items in place.
Multiple Use Cases
splice = edit
splice removes or inserts items in place.
It mutates the original array.
When to Use
Use slice when you want immutability.
Use splice when you must update the array itself.
More Examples
3. splice insert
const items = ["a", "d"];
items.splice(1, 0, "b", "c");
console.log(items); // ["a", "b", "c", "d"]splice can insert items.
4. slice with negative
const items = ["a", "b", "c", "d"];
const lastTwo = items.slice(-2);
console.log(lastTwo); // ["c", "d"]Negative indexes count from the end.
Comparison
Without
const items = [1, 2, 3];
items.splice(1, 1); // mutatesWith
const items = [1, 2, 3];
const copy = items.slice(1, 2); // no mutationCommon Mistakes and Fixes
Using slice when you need mutation
Use splice to change the original array.
Using splice when you need immutability
Use slice to copy instead of mutate.
Forgetting splice returns removed items
splice returns the removed elements, not the array.
Interview Questions
What is the main difference?
slice copies, splice mutates.
What does splice return?
An array of removed elements.
When should you use slice?
When you want immutability.
Practice Problem
Practice: Remove the middle element from an array using splice.
const nums = [1, 2, 3, 4, 5];
// TODO: remove 3
One Possible Solution
const nums = [1, 2, 3, 4, 5];
nums.splice(2, 1);
console.log(nums);Frequently Asked Questions
Does slice mutate?
No, slice returns a new array.
Does splice mutate?
Yes, splice changes the original array.
Can splice insert and remove?
Yes, it can do both in one call.
Try It Yourself
Try editing the indexes to see how results change.