what are watchers in vuejs code example
Example: vue add watcher
vm.$watch('person.name.firstName', function(newValue, oldValue) {
alert('First name changed from ' + oldValue + ' to ' + newValue + '!');
});
vm.$watch('person.name.firstName', function(newValue, oldValue) {
alert('First name changed from ' + oldValue + ' to ' + newValue + '!');
});