A bit of research indicates that there is no way to detect when Cancel is selected in the File Selection dialog window. You can use onchange or onblur to check if files have been selected or if something has been added to the input value.

This could look like: https://jsfiddle.net/Twisty/j18td9cs/

HTML

<form>

  Select File:

  <input type=file name=test1 id=testFile />

  <button type=reset id=pseudoCancel>

    Cancel

  </button>

</form>

JavaScript

var inputElement = document.getElementById(testFile);

var cancelButton = document.getElementById(pseudoCancel);

var numFiles = 0;



inputElement.onclick = function(event) {

  var target = event.target || event.srcElement;

  console.log(target, clicked.);

  console.log(event);

  if (target.value.length == 0) {

    console.log(Suspect Cancel was hit, no files selected.);

    cancelButton.onclick();

  } else {

    console.log(File selected: , target.value);

    numFiles = target.files.length;

  }

}



inputElement.onchange = function(event) {

  var target = event.target || event.srcElement;

  console.log(target, changed.);

  console.log(event);

  if (target.value.length == 0) {

    console.log(Suspect Cancel was hit, no files selected.);

    if (numFiles == target.files.length) {

      cancelButton.onclick();

    }

  } else {

    console.log(File selected: , target.value);

    numFiles = target.files.length;

  }

}



inputElement.onblur = function(event) {

  var target = event.target || event.srcElement;

  console.log(target, changed.);

  console.log(event);

  if (target.value.length == 0) {

    console.log(Suspect Cancel was hit, no files selected.);

    if (numFiles == target.files.length) {

      cancelButton.onclick();

    }

  } else {

    console.log(File selected: , target.value);

    numFiles = target.files.length;

  }

}





cancelButton.onclick = function(event) {

  console.log(Pseudo Cancel button clicked.);

}

I suggest making your own cancel or reset button that resets the form or clears the value from the input.