Validate comma separated email id's

I have a multiline textbox which accepts email id's as the input.
Now I want to validate this textbox using javascript so that correct email ids are entered.
 - If the dont enter any email, error "Email Required"
 - They may enter single or multiple email id's
 - Multiple email id's must be separated by a comma.
 - User may enter one email per line.
Can anyone help me with the javascript function for the above. I wrote some function but was not successfull in writing a one for multiple email id's.
Any help would be appreciated.
Thanks

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