[Term Entry] JavaScript Strings: lastIndexOf()

content/javascript/concepts/strings/terms/lastIndexOf/lastIndexOf.md

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+---
+Title: '.lastIndexOf()'
+Description: 'Returns the index of the last occurrence of a specified substring within a string, or -1 if the substring is not found.'
+Subjects:
+- 'Computer Science'
+- 'Web Development'
+Tags:
+- 'Strings'
+- 'Methods'
+- 'JavaScript'
+CatalogContent:
+- 'learn-javascript'
+- 'paths/web-development'
+---
+
+The **`.lastIndexOf()`** method in JavaScript returns the position of the last occurrence of a specified substring within a [string](https://www.codecademy.com/resources/docs/javascript/strings). If the substring is not found, it returns `-1`. It performs a case-sensitive search and can take an optional starting position from which to begin the search backwards.
+
+## Syntax
+
+```pseudo
+string.lastIndexOf(searchValue, fromIndex)
+```
+
+**Parameters:**
+
+- `searchValue`: The substring to search for.
+- `fromIndex` (optional): The position to start searching backward from. Defaults to the string’s length.
+
+**Return value:**
+
+Returns an integer representing the index of the last occurrence of the specified substring within the string. If the substring isn’t found, it returns `-1`.
+
+## Example 1: Finding the Last Mention of a Name
+
+In this example, a chat message contains multiple mentions of a person’s name, and the method finds the last one:
+
+```js
+const message = 'Hey Sam, Sam, are you coming to the meeting, Sam?';
+const lastSam = message.lastIndexOf('Sam');
+console.log(lastSam);
+```
+
+The output of this code is:
+
+```shell
+45
+```
+
+## Example 2: Searching Backward from a Certain Point
+
+In this example, the search begins from a specific index to locate the previous occurrence of a keyword:
+
+```js
+const report = 'Error at line 23. Warning at line 45. Error again at line 78.';
+const prevError = report.lastIndexOf('Error', 40);
+console.log(prevError);
+```
+
+The output of this code is:
+
+```shell
+0
+```
+
+## Codebyte Example: Locating the Last Hashtag in a Social Media Caption
+
+In this example, a caption includes multiple hashtags, and the method identifies the position of the last one:
+
+```codebyte/javascript
+const caption = 'Just finished a 10k run! #fitness #running #motivation';
+const lastHashtag = caption.lastIndexOf('#');
+console.log(lastHashtag);
+```