JavaScript/REGEX: Validate email addresses separated by commas

I use this JavaScript code to validate an email address:

var e = 'email@example.com';
if(/^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/.test(e) == false) alert('Fail');

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How can I test to see if any email addresses, separated by commas, are invalid?

For example, this should pass:
test@example.com, xyy@example.com, hello@example.com

But this should fail:
test@example.com, xyy, hello@example.com