It has been already said that the eldritch blast is an attack with separate spell attack rolls on each beam
The PHB states:
You can direct the beams at the same target or at different ones. Make a separate attack roll for each beam.
But what happens when you ready an action with an eldritch blast? You can't do multiple attacks on a readied action, I can't find any rules that contradicts that the eldritch blast can be used at its full potential on a readied action.