phpjs/functions/strings/strpos.js

php.js offers community built php functions in javascript

function strpos(haystack, needle, offset) {
  //  discuss at: http://phpjs.org/functions/strpos/
  // original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // improved by: Onno Marsman
  // improved by: Brett Zamir (http://brett-zamir.me)
  // bugfixed by: Daniel Esteban
  //   example 1: strpos('Kevin van Zonneveld', 'e', 5);
  //   returns 1: 14

  var i = (haystack + '')
    .indexOf(needle, (offset || 0));
  return i === -1 ? false : i;
}