Array.prototype.slice()
The slice()
method 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
Optional-
Zero-based index at which to start extraction.
A negative index can be used, indicating an offset from the end of the sequence.
slice(-2)
extracts the last two elements in the sequence.If
start
is undefined,slice
starts from the index0
.If
start
is greater than the index range of the sequence, an empty array is returned. end
Optional-
Zero-based index before which to end extraction.
slice
extracts up to but not includingend
. For example,slice(1,4)
extracts the second element through the fourth element (elements indexed 1, 2, and 3).A negative index can be used, indicating an offset from the end of the sequence.
slice(2,-1)
extracts the third element through the second-to-last element in the sequence.If
end
is omitted,slice
extracts through the end of the sequence (arr.length
).If
end
is greater than the length of the sequence,slice
extracts through to the end of the sequence (arr.length
).
Return value
A new array containing the extracted elements.
Description
slice
does not alter the original array. It returns a shallow copy of
elements from the original array. Elements of the original array are copied into the
returned array as follows:
-
For objects,
slice
copies object references into the new array. Both the original and new array refer to the same object. If an object changes, the changes are visible to both the new and original arrays. -
For strings, numbers and booleans (not
String
,Number
andBoolean
objects),slice
copies the values into the new array. Changes to the string, number, or boolean in one array do not affect the other array.
If a new element is added to either array, the other array is not affected.
Examples
Return a portion of an existing array
let fruits = ['Banana', 'Orange', 'Lemon', 'Apple', 'Mango']
let 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.
let myHonda = { color: 'red', wheels: 4, engine: { cylinders: 4, size: 2.2 } }
let myCar = [myHonda, 2, 'cherry condition', 'purchased 1997']
let newCar = myCar.slice(0, 2)
// Display the values of myCar, newCar, and the color of myHonda
// referenced from both arrays.
console.log('myCar = ' + JSON.stringify(myCar))
console.log('newCar = ' + JSON.stringify(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)
// Display the color of myHonda referenced from both arrays.
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
Array-like objects
slice
method can also be called to convert Array-like objects/collections
to a new Array. You just bind
the method to the
object. The arguments
inside a function is an
example of an 'array-like object'.
function list() {
return Array.prototype.slice.call(arguments)
}
let list1 = list(1, 2, 3) // [1, 2, 3]
Binding can be done with the call()
method of
Function
and it can also be reduced using
[].slice.call(arguments)
instead of
Array.prototype.slice.call
.
Anyway, it can be simplified using bind
.
let unboundSlice = Array.prototype.slice
let slice = Function.prototype.call.bind(unboundSlice)
function list() {
return slice(arguments)
}
let list1 = list(1, 2, 3) // [1, 2, 3]
Specifications
Specification |
---|
ECMAScript Language Specification # sec-array.prototype.slice |
Browser compatibility
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