Show Diff with Copy of Destination Text

For a web application I needed to show the difference between two texts.
First I tried calculating this in the backend (Python) but using fast-diff in Javascript was easier.
The important part here was the possibility to mark and copy only the destination part of the difference.

The result of a diff call is a list of tuples: "equal (0), insert (+1), delete (-1)" and the character at this position.
Now every change is added with either <span> or with <del>.
All <del> segements are not part of the marking when copied.
The color classes are for Bulma (yellow background for inserts, red strikethrough for deletes).

Example code:
var difference = diff("abc", "ace");
// result: [[0, 'a'], [-1, 'b'], [0, 'c'], [1, 'e']]
var r = ""
difference.forEach(e => {
  if (e[0] == 0) {
    r = r + e[1];
  } else if (e[0] == 1) {
    r = r + '<span class="has-background-warning">' + e[1] + "</span>";
  } else if (e[0] == -1) {
    r = r + '<del class="has-text-danger">' + e[1] + "</del>";
// "a<del class="has-text-danger">b</del>c<span class="has-background-warning">e</span>"
Example rendered:


The first line is the rendered string and the second line is the same rendered string marked. Important here, the <del> part is not part of the marking.