phpjs/functions/strings/strrpos.js

php.js offers community built php functions in javascript

function strrpos(haystack, needle, offset) {
  //  discuss at: http://phpjs.org/functions/strrpos/
  // original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // bugfixed by: Onno Marsman
  // bugfixed by: Brett Zamir (http://brett-zamir.me)
  //    input by: saulius
  //   example 1: strrpos('Kevin van Zonneveld', 'e');
  //   returns 1: 16
  //   example 2: strrpos('somepage.com', '.', false);
  //   returns 2: 8
  //   example 3: strrpos('baa', 'a', 3);
  //   returns 3: false
  //   example 4: strrpos('baa', 'a', 2);
  //   returns 4: 2

  var i = -1;
  if (offset) {
    i = (haystack + '')
      .slice(offset)
      .lastIndexOf(needle); // strrpos' offset indicates starting point of range till end,
    // while lastIndexOf's optional 2nd argument indicates ending point of range from the beginning
    if (i !== -1) {
      i += offset;
    }
  } else {
    i = (haystack + '')
      .lastIndexOf(needle);
  }
  return i >= 0 ? i : false;
}