var element = document.createElement('input');

element.setAttribute('type','email');

element.value = 'foo@foo.com';

console.log(element.validity.valid);

​

var elm;

function isValidEmail(s) {

  if(!elm) {

    elm = document.createElement('input');

    elm.setAttribute('type', 'email');

    console.log('made elm');

  }

  elm.value = s;

  return elm.validity.valid;

}

​

console.log(isValidEmail('foo'));

console.log(isValidEmail('goo@goo.com'));

console.log(isValidEmail('zoo'));