Fixes incorrect, specified, file extensions in a specified directory

extension_fixer.js

/* usage: `node extension_fixer.js ext-name (/)sub-folder */
/* sub folder is optional. */
/**
 * Goes over all files in the current directory
 *  - checks if they have an incorrect extension name
 *  - prints out the conflict 
 *  - changes their file name.
 *  --- Limitations:
 *  Only fixes letter-case conflicts.
 */

const fs = require('fs');
const path = require('path'); 
var dext = process.argv[2];
var dir = __dirname + ( process.argv[3] || "" );

fs.readdir(dir, (err, files) => {
  files.forEach(file => {
    var res = file.split('.');
    if( res[1] !== dext && res[1].toLowerCase() === dext ){
        var fix = res[0] + '.' + dext;
        console.log("ext-error: \"", file, "\"");
        console.log("\tfixing to: \"", fix , "\"")
        fs.rename( file, fix, function(err) {
             if ( err ) console.log('RENAME ERROR: ' + err);
        });
    }
  });
});