Hi,
There are 2 ways possible to assign vlans to an interface in JUNOS:
1. Under edit vlans vlan-name -> set interface x/x/x
2. Under edit interfaces x/x/x unit 0 family ethernet-switching -> set vlan members vlan-name
With method 1, if you have multiple vlans on same group of interfaces you could use copy vlan xxx to vlan yyy. The vlan-id will need to be changed but the interfaces will be copied.
In Junos EX config, the vlan-name is the reference for the vlan.
Cheers,
Ashvin