phpjs/functions/var/is_string.js

php.js offers community built php functions in javascript

function is_string(mixed_var) {
  // From: http://phpjs.org/functions
  // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // *     example 1: is_string('23');
  // *     returns 1: true
  // *     example 2: is_string(23.5);
  // *     returns 2: false
  return (typeof mixed_var === 'string');
}