5. What is the purpose of the array slice method?

The slice() method in JavaScript is used to create a shallow copy of a portion of an array without modifying the original array. It returns a new array containing the selected elements.

Syntax

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array.slice(start, end)

Parameters

• start (optional): The index where extraction begins (inclusive). If omitted, it defaults to 0.
• end (optional): The index where extraction stops (exclusive). If omitted, it defaults to the length of the array.

Examples

1. Extracting part of an array

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let numbers = [1, 2, 3, 4, 5];
let sliced = numbers.slice(1, 4); // Extracts elements from index 1 to 3 (4 is excluded)
console.log(sliced); // [2, 3, 4]
console.log(numbers); // [1, 2, 3, 4, 5] (original array remains unchanged)

2. Copying an entire array

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let arr = [10, 20, 30];
let copy = arr.slice(); 
console.log(copy); // [10, 20, 30]

3. Using negative indices

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let arr = ['a', 'b', 'c', 'd', 'e'];
console.log(arr.slice(-3)); // ['c', 'd', 'e'] (last 3 elements)
console.log(arr.slice(-4, -1)); // ['b', 'c', 'd']

Key Points

• slice() does not modify the original array.
• It can be used to copy arrays or extract portions of them.
• Supports negative indices for selecting elements from the end.

Comparison: slice() vs splice() in JavaScript

Examples

1. slice() (Non-destructive)

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let arr = [1, 2, 3, 4, 5];
let sliced = arr.slice(1, 4); // Extract elements from index 1 to 3
console.log(sliced); // [2, 3, 4]
console.log(arr); // [1, 2, 3, 4, 5] (unchanged)

2. splice() (Destructive)

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let arr = [1, 2, 3, 4, 5];
let spliced = arr.splice(1, 3); // Remove 3 elements starting from index 1
console.log(spliced); // [2, 3, 4] (removed elements)
console.log(arr); // [1, 5] (modified array)

3. Using splice() to add elements

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let arr = [1, 2, 5];
arr.splice(2, 0, 3, 4); // Insert 3, 4 at index 2
console.log(arr); // [1, 2, 3, 4, 5]

When to Use?

• Use slice() when you only need to extract elements without modifying the original array.
• Use splice() when you need to remove, replace, or insert elements in the original array.