function isEmail(value) {

  var pattern = /((([A-Za-z]{3,9}:(?:\/\/)?)(?:[\-;:&=\+\$,\w]+@)?[A-Za-z0-9\.\-]+|(?:www\.|[\-;:&=\+\$,\w]+@)[A-Za-z0-9\.\-]+)((?:\/[\+~%\/\.\w\-_]*)?\??(?:[\-\+=&;%@\.\w_]*)#?(?:[\.\!\/\\\w]*))?)/;

  return pattern.test(value);

}

​

const emails = [

  'Abc\@def@example.com',

  'Fred\ Bloggs@example.com',

  'Joe.\\Blow@example.com',

  '"Abc@def"@example.com',

  '"Fred Bloggs"@example.com',

  'customer/department=shipping@example.com',

  '$A12345@example.com',

  '!def!xyz%abc@example.com',

  '_somename@example.com'

];

​

emails.forEach(email => console.log(email, isEmail(email)) );