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In a system, files often need to be fetched or processed asynchronously. Given a prepare_file function, which takes a path and a callback, write a process_files function which takes an array of paths, applies prepare_file to each element, and returns the array of results to a provided callback. The result array should be in the same order as the input array.

Below is a function stub for prepare_file, which simulates an asynchronous task for processing the provided path, and returning the result. (The actual prepare_file function implementation should be considered a black box when implementing process_files.)

      function prepare_file(path, callback) {
       setTimeout(function () {
         callback(path + "_found");
       }, 1000*Math.random());
      };

Example use of prepare_file:

      prepare_file('a', function (path) {
       // path should equal 'a_found'
      });

Example use of process_files:

      process_files(['a', 'b', 'c'], function (paths) {
       // paths should equal ['a_found', 'b_found', 'c_found']
      });

Answers may be in JavaScript or CoffeeScript and should assume the presence of a global prepare_file function (you can use the prepare_file stub above for testing your solution). You shouldn’t use any other libraries.

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You can also call Jake on 07791 068 122 to discuss your application.