Extracting Part of an Array

Extracting part of an Array: `slice()`

The slice() method in JavaScript extracts a section of an array and returns it as a new array without modifying the original array. This method is helpful when working with a portion of an array without affecting the original one.

The slice() function takes two arguments: the start index (inclusive) and the end index (exclusive). The range defined by these indices is used to select elements from the array.

//Syntax
slice(start)
slice(start, end)

`start`: The index at which to start extracting elements (inclusive). If not provided, `slice()` starts from index `0`.
`end`: (Optional) The index at which to stop extracting elements (exclusive). If not provided, `slice()` extracts up to the end of the array.

Examples

Example 1, using slice() to extract a subarray:

const animals = ['dog', 'cat', 'elephant', 'giraffe', 'lion']

const subArray = animals.slice(1, 4)
console.log(subArray) // Output: ['cat', 'elephant', 'giraffe']

In this example:

The start index is 1 (which is “cat”), and the end index is 4 (which is “lion”, but since the end index is exclusive, it’s not included).
The extracted subarray includes the elements from index 1 to 3.

Example 2, using slice() with only the start index:

const fruits = ['apple', 'banana', 'cherry', 'date', 'elderberry']

const subArrayFromIndex = fruits.slice(2)
console.log(subArrayFromIndex) // Output: ['cherry', 'date', 'elderberry']

In this case, by providing only the start index (2), slice() extracts all elements from index 2 to the end of the array.

Example 3, using slice() with negative indices:

const colors = ['red', 'blue', 'green', 'yellow', 'purple']

const lastTwo = colors.slice(-2)
console.log(lastTwo) // Output: ['yellow', 'purple']

Negative indices can be used with slice(). A negative start index counts from the end of the array, so -2 refers to the second-to-last element, and the extraction continues to the end.

Notes

Non-destructive: The slice() method does not modify the original array.
Empty array: If the start index is greater than or equal to the array length, or if the start index is greater than the end index, slice() returns an empty array.
Omitting arguments: If both start and end are omitted, slice() returns a shallow copy of the entire array.
The slice() method returns a shallow copy of a portion of an array into a new array object.
The slice() method can take no arguments: the start index is 0 and the end index is the length of the array.

Extracting Part of an Array