Need a basename function in Javascript

Question

I need a short basename function (one-liner ?) for Javascript:

basename(\"/a/folder/file.a.ext\") -> \"file.a\"
basename(\"/a/folder/file.ext\") -> \"f         


        

Answer 1

Contrary to misinformation provided above, regular expressions are extremely efficient. The caveat is that, when possible, they should be in a position so that they are compiled exactly once in the life of the program.

Here is a solution that gives both dirname and basename.

const rx1 = /(.*)\/+([^/]*)$/;    // (dir/) (optional_file)
const rx2 = /()(.*)$/;            // ()     (file)

function dir_and_file(path) {
  // result is array with
  //   [0]  original string
  //   [1]  dirname
  //   [2]  filename
  return rx1.exec(path) || rx2.exec(path);
}
// Single purpose versions.
function dirname(path) {
  return (rx1.exec(path) || rx2.exec(path))[1];
}
function basename(path) {
  return (rx1.exec(path) || rx2.exec(path))[2];
}

As for performance, I have not measured it, but I expect this solution to be in the same range as the fastest of the others on this page, but this solution does more. Helping the real-world performance is the fact that rx1 will match most actual paths, so rx2 is rarely executed.

Here is some test code.

function show_dir(parts) {
  console.log("Original str :"+parts[0]);
  console.log("Directory nm :"+parts[1]);
  console.log("File nm      :"+parts[2]);
  console.log();
}
show_dir(dir_and_file('/absolute_dir/file.txt'));
show_dir(dir_and_file('relative_dir////file.txt'));
show_dir(dir_and_file('dir_no_file/'));
show_dir(dir_and_file('just_one_word'));
show_dir(dir_and_file('')); // empty string
show_dir(dir_and_file(null)); 

And here is what the test code yields:

# Original str :/absolute_dir/file.txt
# Directory nm :/absolute_dir
# File nm      :file.txt
# 
# Original str :relative_dir////file.txt
# Directory nm :relative_dir
# File nm      :file.txt
# 
# Original str :dir_no_file/
# Directory nm :dir_no_file
# File nm      :
# 
# Original str :just_one_word
# Directory nm :
# File nm      :just_one_word
# 
# Original str :
# Directory nm :
# File nm      :
# 
# Original str :null
# Directory nm :
# File nm      :null

By the way, "node" has a built in module called "path" that has "dirname" and "basename". Node's "path.dirname()" function accurately imitates the behavior of the "bash" shell's "dirname," but is that good? Here's what it does:

1. Produces '.' (dot) when path=="" (empty string).
2. Produces '.' (dot) when path=="just_one_word".
3. Produces '.' (dot) when path=="dir_no_file/".

I prefer the results of the function defined above.