Detect copy/paste in HTML form under .NET CORE MVC 2.1

Question

I am working on a project that already existed when I arrived at the company.

Users need to paste several ISBN numbers from Excel to a search field in my Index page (HTML). They do so by selecting many ISBNs from Excel and copy/paste into the search field. The problem is that sometimes ISBNs are poorly formatted and may have a letter or special symbol in the middle (don’t ask me why, no idea).

The string resembles to something like this:

3356565663541 3356565663541 3356565663541 3356B565663541 3356565663541A

The code in my index page for the input form is:

<div class="col-lg-4">
  <div class="form-group">
    <label>ISBN</label>
    <input asp-for="Advanced_ISBN" id="ISBN" type="text" placeholder="" class="form-control">
  </div>
</div>

I need a way to analyze what is pasted into the text box and signal to the user that something is wrong.

I'd like to do that in C# if possible but I have no idea on how to:

Detect the "paste into the textbox" with the ctr-v or right click, past;
Get the string to analyze it;
Show it on a new temporary window with highlighted color on the line that may contain an error.

Users would press OK if everything is correct or detect the line that is NOK.

Sounds like you want to use client-side detection, I suggest you to read this example first: https://stackoverflow.com/questions/2903991/how-to-detect-ctrlv-ctrlc-using-javascript. Note that the server-side code doesn't know if the text contained inside textbox is a result of copying and pasting verbatim. — Tetsuya Yamamoto, Dec 12 '18 at 09:29

mplungjan · Answer 1 · 2018-12-12T10:09:08.563

Use the input event handler. It will trigger on typing and on pasting both

jQuery:

$("ISBN").on("input",function() {});

plain JS:

document.getElementById("ISBN").addEventListener("input",function() {});

function isValidISBN (isbn) { // from https://neilang.com/articles/how-to-check-if-an-isbn-is-valid-in-javascript/
  isbn = isbn.replace(/[^\dX]/gi, '');
  if(isbn.length != 10){
    return false;
  }
  var chars = isbn.split('');
  if(chars[9].toUpperCase() == 'X'){
    chars[9] = 10;
  }
  var sum = 0;
  for (var i = 0; i < chars.length; i++) {
    sum += ((10-i) * parseInt(chars[i]));
  };
  return ((sum % 11) == 0);
}

document.getElementById("ISBN").addEventListener("input",function() {
  this.value.split(" ").forEach(function(val) {
    if(val.trim()) console.log(val,isValidISBN(val));
  });
});

A valid ISBN would be 0-85131-041-9

<div class="col-lg-4">
  <div class="form-group">
    <label>ISBN</label>
    <input asp-for="Advanced_ISBN" id="ISBN" type="text" placeholder="" class="form-control">
  </div>
</div>

If you insist on having the server process it, do this (here jQuery):

$("#ISBN").on("input",function() {
  $.post("yourcsharpprocess",{ data : this.value },function(data) {
    $("#result").html(data);
  });
});

I don't want a standard code, i need to send the string into C# and to load it into a window. How can i call a C# method from HTML and send it the string? Thank you. — Rui Ruivo, Dec 12 '18 at 09:58
@RuiRuivo: What you want to achieve according to **your question** is exactly what this answer tells you. You don't need to send it to the server, just to validate if an ISBN has a valid syntax (it even validates the checksum letter, which should catch most of the errors where two numbers are swapped) — Tseng, Dec 12 '18 at 10:04
Yeah, why wait for a round trip - C# cannot detect a paste - I have updated the answer — mplungjan, Dec 12 '18 at 10:09

Detect copy/paste in HTML form under .NET CORE MVC 2.1

1 Answers1