In this JavaScript tutorial we’re going to learn about the includes() JavaScript Array Method and how it can be used to find out if a value is inside an array.
This method will return either true or false.
The **includes()**
method determines whether an array includes a certain value among its entries, returning true
or false
as appropriate.
const array1 = [1, 2, 3];
console.log(array1.includes(2));
// expected output: true
const pets = ['cat', 'dog', 'bat'];
console.log(pets.includes('cat'));
// expected output: true
console.log(pets.includes('at'));
// expected output: false
arr.includes(valueToFind[, fromIndex])
valueToFind
The value to search for.
Note: When comparing strings and characters, includes()
is case-sensitive.
fromIndex
| Optional
The position in this array at which to begin searching for valueToFind
.
The first character to be searched is found at fromIndex
for positive values of fromIndex
, or at arr.length + fromIndex
for negative values of fromIndex
(using the absolute value of fromIndex
as the number of characters from the end of the array at which to start the search).
Defaults to 0
.
A Boolean
which is true
if the value valueToFind
is found within the array (or the part of the array indicated by the index fromIndex
, if specified).
Values of zero are all considered to be equal, regardless of sign. (That is, -0
is considered to be equal to both 0
and +0
), but false
is not considered to be the same as 0
.
Note: Technically speaking, includes()
uses the sameValueZero
algorithm to determine whether the given element is found.
[1, 2, 3].includes(2) // true
[1, 2, 3].includes(4) // false
[1, 2, 3].includes(3, 3) // false
[1, 2, 3].includes(3, -1) // true
[1, 2, NaN].includes(NaN) // true
fromIndex
is greater than or equal to the array lengthIf fromIndex
is greater than or equal to the length of the array, false
is returned. The array will not be searched.
let arr = ['a', 'b', 'c']
arr.includes('c', 3) // false
arr.includes('c', 100) // false
If fromIndex
is negative, the computed index is calculated to be used as a position in the array at which to begin searching for valueToFind
. If the computed index is less or equal than -1 * arr.length
, the entire array will be searched.
// array length is 3
// fromIndex is -100
// computed index is 3 + (-100) = -97
let arr = ['a', 'b', 'c']
arr.includes('a', -100) // true
arr.includes('b', -100) // true
arr.includes('c', -100) // true
arr.includes('a', -2) // false
includes()
used as a generic methodincludes()
method is intentionally generic. It does not require this
value to be an Array object, so it can be applied to other kinds of objects (e.g. array-like objects).
The example below illustrates includes()
method called on the function’s arguments object.
(function() {
console.log([].includes.call(arguments, 'a')) // true
console.log([].includes.call(arguments, 'd')) // false
})('a','b','c')
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