Java Script Array indexOf()
In this tutorial, we will learn about the JavaScript Array indexOf()
method with the help of examples.
The
indexOf()
method returns the first index of occurance of an array element, or-1
if it is not found.
Syntax
arr.indexOf(searchValue, fromIndex)
- Here
arr
is an Array
Parameters
searchValue
( required ) – The element to locate in the array.fromIndex
(optional) – Theindex
to start the search at. By default, it is .
Return Value
A Number
– The first position where the search-value occurs.- Returns
-1
if the element is not found in the array.
indexOf()
method uses the strict equality comparison algorithm (similar to the triple-equals operator or===
) comparessearchValue
Using indexOf() method example
const countries = ["UK", "USA", "Germany", "Spain"]; console.log(countries.indexOf("USA")); console.log(countries.indexOf("Spain"));
OutPut
1 3
No Occurrence is Found
const countries = ["UK", "USA", "Germany", "Spain"]; // if not found , returns -1 console.log(countries.indexOf("Italy"));
Output
-1
Suppose, you have an array marks
that consists of six numbers
const marks = [ 11, 22, 33, 44, 55, 66 ];
The indexOf()
method to find the elements in the marks
array
console.log(marks.indexOf(11)); // 0 console.log(marks.indexOf(44)); // 3 console.log(marks.indexOf(66)); // 5 console.log(marks.indexOf(33)); // 2 console.log(marks.indexOf(22)); // 1 console.log(marks.indexOf(55)); // 4
Case Sensitive
The
indexOf()
is case-sensitive. Lets See the example
const countries = ["UK", "USA", "Germany", "Spain"]; // case-senstive console.log(countries.indexOf("usa")); // -1
To Overcome , You can convert string in an array to lowercase before using the
indexOf()
method.
const countries = ["UK", "USA", "Germany", "Spain"]; // Convert Each Item to LowerCase const sameCaseCountries = countries.map((e) => e.toLowerCase()); console.log(sameCaseCountries.indexOf("usa".toLowerCase())); console.log(sameCaseCountries.indexOf("SpAin".toLowerCase()));
Output
1 3