phpjs/functions/strings/stripos.js

php.js offers community built php functions in javascript

function stripos(f_haystack, f_needle, f_offset) {
  //  discuss at: http://phpjs.org/functions/stripos/
  // original by: Martijn Wieringa
  //  revised by: Onno Marsman
  //   example 1: stripos('ABC', 'a');
  //   returns 1: 0

  var haystack = (f_haystack + '')
    .toLowerCase();
  var needle = (f_needle + '')
    .toLowerCase();
  var index = 0;

  if ((index = haystack.indexOf(needle, f_offset)) !== -1) {
    return index;
  }
  return false;
}