How Can I Efficiently Determine File Extensions in JavaScript?

Obtaining File Extensions Using JavaScript

Determining the extension of a file is a valuable skill in web programming. Suppose we have the following code that aims to retrieve the extension for the filenames "50.xsl" and "30.doc."

var file1 = "50.xsl";
var file2 = "30.doc";
getFileExtension(file1); //returns xsl
getFileExtension(file2); //returns doc

function getFileExtension(filename) {
    /*TODO*/
}

Efficient Approach

A concise and efficient method to obtain the extension is by utilizing the split() function to divide the filename into its components:

return filename.split('.').pop();

This approach splits the filename based on the period ('.') character and returns the last component, representing the file extension.

Alternative Solution

Alternatively, we can use a regular expression to match and capture the file extension:

return /[^.]+$/.exec(filename);

This regular expression matches any sequence of characters after the final period in the filename, effectively capturing the extension.

Preventing Errors

To prevent errors when no period is present in the filename, we can modify the regular expression as follows:

return (/[.]/.exec(filename)) ? /[^.]+$/.exec(filename) : undefined;

This modified expression checks for the presence of a period and returns an undefined value if none is found.

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