how to add a random string between filename and file extension in JavaScript in one line?

Question

I want to add a hashstring to file name, so I'm trying to rename the string.

This is what I have:

var x = "puh.jpg";
var y = x.split(".");
y.splice(1,0,"foo");
var z = y.join(".");
console.log(z)

Which correctly returns: puh.foo.jpg.

Question:
Can this be done in a single line and without having to declare helper variables?

Thanks!

Answer 1

You can do it with a regex pretty easily (modulo the complexity of names you need to work with):

var y = x.replace(/^([^.]*)\.(.*)$/, '$1.foo.$2');

In the regular expression, I've used ( ) to create groups (2 of them). The first group matches all the characters in the name except for periods, up to the . separating the name from the file extension. (If the extension might not be present at all, then it would look like ^([^.]*)\.?(.*)$ instead, to make the "." optional.) The second group gets the rest of the name (the extension).

In the replacement string, the constructs "$1" and "$2" are expanded to be the parts of the original string matched by the two groups.

Answer 2

Use this one. It guarantees that the string is injected at the last dot of the file name. It also works if there is no extension.

alert(x.replace(/(\.[^\.]*)?$/, '.foo$1'))

Try it with:

puh.jpg (=> puh.foo.jpg)
puh.bar.jpg (=> puh.bar.foo.jpg)
foo_bar (=> foo_bar.foo)
foo_bar. (=> foo_bar.foo.)

To explain:

• \. matches a dot
• [^\.] matches any character other than the dot
• \.[^\.]* matches a dot followed by zero or more non-dot characters
• \.[^\.]*$ matches a dot followed by zero or more non-dot characters at the end of the string
• (\.[^\.]*)$ matches a dot followed by zero or more non-dot characters at the end and allows the dot and the characters to be referred to as a group with $1
• '.foo$1' replaces the matched characters with .foo followed by the characters themselves

http://jsfiddle.net/HALf6/

Answer 3

x.replace(/\.([a-zA-Z0-9]*)$/, '.foo.$1')