Javascript regex for matching/extracting file extension

Question

The following regex

var patt1=/[0-9a-z]+$/i;

extracts the file extension of strings such as

filename-jpg
filename#gif
fil         


        

Answer 1

Try

var patt1 = /\.([0-9a-z]+)(?:[\?#]|$)/i;

This RegExp is useful for extracting file extensions from URLs - even ones that have ?foo=1 query strings and #hash endings.

It will also provide you with the extension as $1.

var m1 = ("filename-jpg").match(patt1);
alert(m1);  // null

var m2 = ("filename#gif").match(patt1);
alert(m2);  // null

var m3 = ("filename.png").match(patt1);
alert(m3);  // [".png", "png"]

var m4 = ("filename.txt?foo=1").match(patt1);
alert(m4);  // [".txt?", "txt"]

var m5 = ("filename.html#hash").match(patt1);
alert(m5);  // [".html#", "html"]

P.S. +1 for @stema who offers pretty good advice on some of the RegExp syntax basics involved.