github-pr-intellegent-select.js

document.querySelectorAll(".diff-table").forEach(table => {
  table.onmouseover = evt => {
    if (evt.target.tagName !== "TD") {
      return;
    }
    const cellIndex = evt.target.cellIndex;
    table
      .querySelectorAll(`tr td.blob-code:nth-child(${cellIndex === 1 ? 2 : 4})`)
      .forEach(el => {
        el.style["userSelect"] = "auto";
      });
    table
      .querySelectorAll(`tr td.blob-code:nth-child(${cellIndex === 1 ? 4 : 2})`)
      .forEach(el => {
        el.style["userSelect"] = "none";
      });
  };
});