How to get File Extension from File Name in JavaScript

Just like any other programming language, you can use JavaScript to work with files.

When you are working with files, one of the most useful things to know is the file's extension.

In this post, we'll learn how to extract the file's extension from the file name in JavaScript.

Extracting the file extension from the file name

To extract the file extension from the file name, we'll use the split() method.

The split() method splits a string into an array of substrings using the parameter as the delimiter, and then returns the substrings as an array.

JAVASCRIPT
const fileName = "my-file.txt";
const fileExtension = fileName.split(".");

console.log(fileExtension);

BASH
(2) ['my-file', 'txt']

From there, we can use the pop() method to get the last element in the array.

Let's see the full example:

JAVASCRIPT
const fileName = "my-file.txt";
const fileExtension = fileName.split(".").pop();

console.log(fileExtension);

BASH
txt

This works because in almost all cases, the file extension is the last part of the file name, after the last dot.

For reusability, we can also turn this into a function:

JAVASCRIPT
const getFileExtension = (fileName) => {
    return fileName.split(".").pop();
}

const fileExtension = getFileExtension("my-file.txt");

console.log(fileExtension);

BASH
txt

Conclusion

In this post, we looked at how to extract the file extension from the file name in JavaScript.

Simply use the split() method to split the file name into an array of substrings by splitting on a ., and then use the pop() method to get the last element in the array, which is usually the accurate file extension.

Thanks for reading!

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