Google Script to generate a UUID in Google Sheets - Forked to include menu that fills in UUIDs for active range

UUID.gs

function getId() {
  /**
   * Imported from https://github.com/kyo-ago/UUID
   * Robbie Mitchell, @superstrong
  */
  
  /**
   * UUID.core.js: The minimal subset of the RFC-compliant UUID generator UUID.js.
   *
   * @fileOverview
   * @author  LiosK
   * @version core-1.0
   * @license The MIT License: Copyright (c) 2012 LiosK.
   */
  
  /** @constructor */
  function UUID() {}
  
  /**
   * The simplest function to get an UUID string.
   * @returns {string} A version 4 UUID string.
   */
  UUID.generate = function() {
    var rand = UUID._gri, hex = UUID._ha;
    return  hex(rand(32), 8)          // time_low
          + "-"
          + hex(rand(16), 4)          // time_mid
          + "-"
          + hex(0x4000 | rand(12), 4) // time_hi_and_version
          + "-"
          + hex(0x8000 | rand(14), 4) // clock_seq_hi_and_reserved clock_seq_low
          + "-"
          + hex(rand(48), 12);        // node
  };
  
  /**
   * Returns an unsigned x-bit random integer.
   * @param {int} x A positive integer ranging from 0 to 53, inclusive.
   * @returns {int} An unsigned x-bit random integer (0 <= f(x) < 2^x).
   */
  UUID._gri = function(x) { // _getRandomInt
    if (x <   0) return NaN;
    if (x <= 30) return (0 | Math.random() * (1 <<      x));
    if (x <= 53) return (0 | Math.random() * (1 <<     30))
                      + (0 | Math.random() * (1 << x - 30)) * (1 << 30);
    return NaN;
  };
  
  /**
   * Converts an integer to a zero-filled hexadecimal string.
   * @param {int} num
   * @param {int} length
   * @returns {string}
   */
  UUID._ha = function(num, length) {  // _hexAligner
    var str = num.toString(16), i = length - str.length, z = "0";
    for (; i > 0; i >>>= 1, z += z) { if (i & 1) { str = z + str; } }
    return str;
  };
  
  /**
   * Returns result to Google Sheet
  */
  var newId = UUID.generate();
  return newId;
}

function fillInUUID() {
  var range = SpreadsheetApp.getActiveSheet().getActiveRange();
  var numRows = range.getNumRows();
  var numCols = range.getNumColumns();
  var writeValues = [];
  
  for (var i = 1; i <= numRows; i++) {
    var row = []
    for (var j = 1; j <= numCols; j++) {
      row.push(getId());
    }
    
    writeValues.push(row);
  }
  
  range.setValues(writeValues);
}

// function onOpen is called when the spreadsheet is opened; adds the menu
function onOpen() {
    var ss = SpreadsheetApp.getActiveSpreadsheet();
    var menuEntries = [{
                       name: "UUID",
                       functionName: "fillInUUID"
                       }];
    ss.addMenu("UUID", menuEntries);
}