In JavaScript, indexOf() is a string method that is used to find the location of a substring in a string. Because the indexOf() method is a method of the String object, it must be invoked through a particular instance of the String class. The index position of first character in a string is always starts with zero. If an element is not present in a string, it returns -1.
Note:
The indexOf() method returns the first index (position) of a specified value.
The indexOf() method returns -1 if the value is not found.
The indexOf() method starts at a specified index and searches from left to right.
Syntax:
array.indexOf(item, start)item: Required.
The value to search for.
start: Optional.
Where to start the search.
Default value is 0.
Negative values start the search from the end of the array.
Example 1:
<!DOCTYPE html>
<html>
<body>
<h2>The indexOf() Method</h2>
<p>IndexOf() returns the position of a specified value in an array:</p>
<p id="demo"></p>
<script>
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let index = fruits.indexOf("Apple");
document.getElementById("demo").innerHTML = index;
</script>
</body>
</html>
Output:
Example 2:
<!DOCTYPE html>
<html>
<body>
<h2>The indexOf() Method</h2>
<p>IndexOf() returns the position of a specified value in an array.</p>
<p id="demo"></p>
<script>
const fruits = ["Banana", "Orange", "Apple", "Mango", "Apple"];
let index = fruits.indexOf("Apple", 3);
document.getElementById("demo").innerHTML = index;
</script>
</body>
</html>Output:
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