If I Help someone and they cast Eldritch Blast do they get advantage only on the first attack roll?

.@JeremyECrawford If I Help someone and they cast Eldritch Blast do they get advantage only on the first attack roll?

— Martin Kling (@Mkjp78) May 3, 2016

The Help action benefits your ally's first attack against the target. #DnD https://t.co/DNepJQmHA9

— Jeremy Crawford (@JeremyECrawford) May 9, 2016