Array.prototype.slice()

The slice() method of Array instances returns a shallow copy of a portion of an array into a new array object selected from start to end (end not included) where start and end represent the index of items in that array. The original array will not be modified.

Syntax

slice()
slice(start)
slice(start, end)

Parameters

start
- : Zero-based index at which to start extraction, converted to an integer.
  - Negative index counts back from the end of the array — if start < 0, start + array.length is used.
  - If start < -array.length or start is omitted, 0 is used.
  - If start >= array.length, nothing is extracted.
end
- : Zero-based index at which to end extraction, converted to an integer. slice() extracts up to but not including end.
  - Negative index counts back from the end of the array — if end < 0, end + array.length is used.
  - If end < -array.length, 0 is used.
  - If end >= array.length or end is omitted, array.length is used, causing all elements until the end to be extracted.
  - If end is positioned before or at start after normalization, nothing is extracted.

Return value

A new array containing the extracted elements.

Description

The slice() method is a copying method. It does not alter this but instead returns a shallow copy that contains some of the same elements as the ones from the original array.

The slice() method preserves empty slots. If the sliced portion is sparse, the returned array is sparse as well.

The slice() method is generic. It only expects the this value to have a length property and integer-keyed properties.

Examples

Return a portion of an existing array

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1, 3);

// fruits contains ['Banana', 'Orange', 'Lemon', 'Apple', 'Mango']
// citrus contains ['Orange','Lemon']

Using slice

In the following example, slice creates a new array, newCar, from myCar. Both include a reference to the object myHonda. When the color of myHonda is changed to purple, both arrays reflect the change.

// Using slice, create newCar from myCar.
const myHonda = {
  color: "red",
  wheels: 4,
  engine: { cylinders: 4, size: 2.2 },
};
const myCar = [myHonda, 2, "cherry condition", "purchased 1997"];
const newCar = myCar.slice(0, 2);

console.log("myCar =", myCar);
console.log("newCar =", newCar);
console.log("myCar[0].color =", myCar[0].color);
console.log("newCar[0].color =", newCar[0].color);

// Change the color of myHonda.
myHonda.color = "purple";
console.log("The new color of my Honda is", myHonda.color);

console.log("myCar[0].color =", myCar[0].color);
console.log("newCar[0].color =", newCar[0].color);

This script writes:

myCar = [
  { color: 'red', wheels: 4, engine: { cylinders: 4, size: 2.2 } },
  2,
  'cherry condition',
  'purchased 1997'
]
newCar = [ { color: 'red', wheels: 4, engine: { cylinders: 4, size: 2.2 } }, 2 ]
myCar[0].color = red
newCar[0].color = red
The new color of my Honda is purple
myCar[0].color = purple
newCar[0].color = purple

Calling slice() on non-array objects

The slice() method reads the length property of this. It then reads the integer-keyed properties from start to end and defines them on a newly created array.

const arrayLike = {
  length: 3,
  0: 2,
  1: 3,
  2: 4,
  3: 33, // ignored by slice() since length is 3
};
console.log(Array.prototype.slice.call(arrayLike, 1, 3));
// [ 3, 4 ]

Using slice() to convert array-like objects to arrays

The slice() method is often used with bind() and call() to create a utility method that converts an array-like object into an array.

// slice() is called with `this` passed as the first argument
const slice = Function.prototype.call.bind(Array.prototype.slice);

function list() {
  return slice(arguments);
}

const list1 = list(1, 2, 3); // [1, 2, 3]

Using slice() on sparse arrays

The array returned from slice() may be sparse if the source is sparse.

console.log([1, 2, , 4, 5].slice(1, 4)); // [2, empty, 4]