What is slice() in JavaScript

What is slice()?

slice() is a method used to copy a portion of an array or string without changing the original.

Think of it like cutting a piece out of a cake — you get the piece, but the original cake stays the same.

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Syntax

array.slice(start, end)
string.slice(start, end)

• start → The index where the extraction begins (inclusive).

  • If omitted → starts from 0.

  • If negative → counts from the end.

• end → The index where extraction stops (exclusive).

  • If omitted → goes till the end.

  • If negative → counts from the end.

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Key Points

1. Does not modify the original array/string.

2. Returns a new array (or string in case of strings).

3. Works with negative indexes.

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Array Examples

1) Basic Usage

const fruits = ["apple", "banana", "cherry", "date"];
const sliced = fruits.slice(1, 3);

console.log(sliced);       // ["banana", "cherry"]
console.log(fruits);       // ["apple", "banana", "cherry", "date"] (unchanged)

Here:

• Starts at index 1 → "banana".

• Stops before index 3 → excludes "date".

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2) Omitting the end

const colors = ["red", "green", "blue", "yellow"];
console.log(colors.slice(2)); // ["blue", "yellow"]

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3) Using Negative Indexes

const numbers = [1, 2, 3, 4, 5];
console.log(numbers.slice(-3));     // [3, 4, 5]
console.log(numbers.slice(1, -1));  // [2, 3, 4]

• -3 → starts from the 3rd last element.

• end = -1 → stops before the last element.

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4) Copying the Whole Array

const arr = [10, 20, 30];
const copy = arr.slice();

console.log(copy); // [10, 20, 30]
console.log(copy === arr); // false (different array in memory)

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String Examples

const text = "JavaScript";
console.log(text.slice(0, 4));  // "Java"
console.log(text.slice(4));     // "Script"
console.log(text.slice(-6));    // "Script"

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Difference between slice() and splice()

Feature	slice()	splice()
Changes original?	❌ No	✅ Yes
Return value	New array with extracted items	Removed items (also modifies the original array)
Usage	Copy part of array/string	Add/remove elements in array

Example:

const nums = [1, 2, 3, 4];
nums.slice(1, 3); // [2, 3]  (nums unchanged)
nums.splice(1, 2); // removes 2 elements starting at index 1 → nums becomes [1, 4]

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Quick Cheat Sheet

• Inclusive start index, exclusive end index.

• Works with arrays and strings.

• Negative index → counts from end.

• Good for copying and non-destructive slicing.