Replaces / with \ in Google Sheets

ReplaceSlashes.gs

function onOpen() {
  const ui = SpreadsheetApp.getUi();
  ui.createMenu('Extras')
  .addItem('Replace / with \\ in selection', 'replaceSlashes')
  .addToUi();
}

function replaceSlashes() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const range = SpreadsheetApp.getActive().getActiveRange();
  const numRows = range.getNumRows();
  const numCols = range.getNumColumns();

  for (let i = 1; i <= numCols; i++) {
    for (let j = 1; j <= numRows; j++) {
      const cell = range.getCell(j, i)
      cell.setValue(cell.getValue().replace(/\//g, "\\"));
    }
  }
}