To get the file extension in a Node.js application, you can use the extname() method from the path built-in module.

Here is an example:

const path = require('path')

path.extname('index.html') // .html
path.extname('name.png')   // .png
path.extname('name.of.months.pdf') // .pdf

The extname() method returns the given path extension from the last occurrence of the . (period) character to the end of the string in the last part of the path.

If there is no . in the last part of the path, or if the path starts with . and is the only . character in the path, an empty string is returned:

path.extname('index.') // .

path.extname('index') // '' (empty string)

path.extname('.index')   // '' (empty string)

path.extname('') // .md

If the path provided is not a string, a TypeError is thrown.

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