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String lastIndexOf() Method with Example in JavaScript

JavaScript String lastIndexOf() Method: Here, we are going to learn about the lastIndexOf() method of String in JavaScript.
Submitted by IncludeHelp, on February 02, 2019

String lastIndexOf() Method

lastIndexOf() is method is a String method, it is used to check whether a substring exists in the given string or not. It returns the last index of the substring from the string where substring exists. If substring does not exist in the string – it returns -1.

Syntax

    String.lastIndexOf(substring, [offset]);

Here, substring is the part of the string to be searched and [offset] is the specific index from where we want to search the substring, it's an optional parameter and it's default value is 0.

Note: Method lastIndexOf() searches backward in the string, see in the example – we passed offset 15 and it returns index 0.

Example

<html>
<head>
<title>JavaScipt Example</title>
</head>

<body>
<script>		
	var str = "Hello friends say Hello";
	
	var substr = "Hello";		
	var index = str.lastIndexOf(substr);
	if(index!=-1)
		document.write(substr + " found at " + index + " position.<br>");
	else
		document.write(substr + " does not exist in the " + str + ".<br>");

	substr = "Hi";
	index = str.lastIndexOf(substr);		
	if(index!=-1)
		document.write(substr + " found at " + index + " position.<br>");
	else
		document.write(substr + " does not exist in the " + str + ".<br>");
	
	//searching from a specific index
	substr = "Hello";
	index = str.lastIndexOf(substr,10);		
	if(index!=-1)
		document.write(substr + " found at " + index + " position.<br>");
	else
		document.write(substr + " does not exist in the " + str + ".<br>");		

	substr = "friends";
	index = str.lastIndexOf(substr,15);		
	if(index!=-1)
		document.write(substr + " found at " + index + " position.<br>");
	else
		document.write(substr + " does not exist in the " + str + ".<br>");					
</script>
</body>
</html>

Output

Hello found at 18 position.
Hi does not exist in the Hello friends say Hello.
Hello found at 0 position.
friends found at 6 position.