Insert a string before the extension in a filename

Question

How can I insert a string before the extension in an image filename? For example, I need to convert this:

../Course/Assess/Responsive_Course_1_1.png

Answer 1

Either $1 match a filename with no extension or $2 match an extension.

filename = filename.replace(/^([^.]+)$|(\.[^.]+)$/i, '$1' + "_large" + '$2');