phpjs/functions/strings/strpos.js

php.js offers community built php functions in javascript

function strpos(haystack, needle, offset) {
  // From: http://phpjs.org/functions
  // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   improved by: Onno Marsman
  // +   bugfixed by: Daniel Esteban
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // *     example 1: strpos('Kevin van Zonneveld', 'e', 5);
  // *     returns 1: 14
  var i = (haystack + '').indexOf(needle, (offset || 0));
  return i === -1 ? false : i;
}