How to remove one specific selected file from input file control

As other people pointed out, FileList is read only. You can get around this by pushing those files into a separate Array though. You can then do whatever you want with that curated list of files. If uploading them to a server is the goal, you can use the FileReader API.

Below is a round about way of completely avoiding needing to modify the FileList.
Steps:

1. Add normal file input change event listener
2. Loop through each file from change event, filter for desired validation
3. Push valid files into separate array
4. Use FileReader API to read files locally
5. Submit valid, processed files to server

Event handler and basic file loop code:

var validatedFiles = [];
$("#fileToUpload").on("change", function (event) {
  var files = event.originalEvent.target.files;
  files.forEach(function (file) {
    if (file.name.matches(/something.txt/)) {
      validatedFiles.push(file); // Simplest case
    } else { 
      /* do something else */
    }
  });
});

Below is a more complicated version of the file loop that shows how you can use the FileReader API to load the file into the browser and optionally submit it to a server as a Base64 encoded blob.

  files.forEach(function (file) {
    if (file.name.matches(/something.txt/)) { // You could also do more complicated validation after processing the file client side
      var reader = new FileReader();
      // Setup listener
      reader.onload = (function (processedFile) {
        return function (e) {
          var fileData = { name : processedFile.name, fileData : e.target.result };

          // Submit individual file to server
          $.post("/your/url/here", fileData);

          // or add to list to submit as group later
          validatedFiles.push(fileData);
        };
      })(file);

      // Process file
      reader.readAsDataURL(file);
    } else { 
      /* still do something else */
    }
  });

A note of caution about using FileReader API. Base64 encoding a file will increase its size by around 30%. If that isn’t acceptable you will need to try something else.