JavaScript – Find Index of Substring in String

To find the index of string searchStr in the string str in JavaScript, call indexOf() method on this string str, and pass the other string searchStr as argument.

indexOf() method returns an integer representing the index of the first occurrence of string searchStr in the string str. If string searchStr is not present in the string str, then indexOf() returns -1.

Syntax

The syntax to find the index of string searchStr in the string str is

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str.indexOf(searchStr)

We can also pass an index fromIndex as second argument. The search for the searchStr in str happens from this fromIndex.

The syntax to find the index of string searchStr in the string str from the position fromIndex is

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str.indexOf(searchStr, fromIndex)

Examples

The following is a quick example to find the index of string searchStr in the string str in JavaScript.

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var str = 'Hello World. Beautiful World.';
var searchStr = 'World';
var result = str.indexOf(searchStr);

In the following example, we take two strings: str and searchStr in script, and find the index of string searchStr in the string str using indexOf() method. We shall display the result in a div.

index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
</head>
<body>
    <div id="output"></div>
    <script>
        var str = 'Hello World. Beautiful World.';
        var searchStr = 'World';
        var index = str.indexOf(searchStr);
        document.getElementById('output').innerHTML = 'Index of first occurrence : ' + index;
    </script>
</body>
</html>

Now, we will pass a value of 10 for the second argument fromIndex.

The following is a quick example to find the index of string searchStr in the string str from the position fromIndex in JavaScript.

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var str = 'Hello World. Beautiful World.';
var searchStr = 'World';
var fromIndex = 10;
var result = str.indexOf(searchStr, fromIndex);

In the following example, we take two strings: str and searchStr in script, and find the index of string searchStr in the string str from the position 10, using indexOf() method.

index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
</head>
<body>
    <div id="output"></div>
    <script>
        var str = 'Hello World. Beautiful World.';
        var searchStr = 'World';
        var fromIndex = 10;
        var index = str.indexOf(searchStr, fromIndex);
        document.getElementById('output').innerHTML = 'Index of first occurrence : ' + index;
    </script>
</body>
</html>

Conclusion

In this JavaScript Tutorial, we learned how to find the index of a substring in this string in JavaScript, using indexOf() method, with examples.