For this type of configuration you'll need to configure DHCP pool in SRX for every VLAN in order to assign IPs dynamically to devices .
Let me give you an example of how to configure and assign each DHCP pool for VLAN (following my latest example):
[edit system services dhcp pool]
set 10.10.0.1/24 address-range low 10.10.0.2 high 10.10.0.100
set 10.10.0.1/24 name-server 1.1.1.1
set 10.10.0.1/24 name-server 2.2.2.2
set 10.10.0.1/24 router 10.10.0.1 << This is the gateway it should be the same as the VLAN inet address
So in this example the 10.10.0.1 is for VLAN id =10 (following my latest example in the previous reply)
It should be the same for other VLANs:
set 10.10.1.1/24 address-range low 10.10.1.2 high 10.10.1.100
set 10.10.1.1/24 name-server 1.1.1.1
set 10.10.1.1/24 name-server 2.2.2.2
set 10.10.1.1/24 router 10.10.1.1
set 10.10.2.1/24 address-range low 10.10.2.2 high 10.10.2.100
set 10.10.2.1/24 name-server 1.1.1.1
set 10.10.2.1/24 name-server 2.2.2.2
set 10.10.2.1/24 router 10.10.2.1
No other configuration needed in the EX device for DHCP ..