Bash - Join Arrays

How to join arrays in Bash Script? Very simple :) Example:

#!/bin/bash

a1=(a b c d) #array 1

a2=(e f g h) #array 2

a=(${a1[@]} ${a2[@]}) #join array

echo ${a[@]}

Output is:

a b c d e f g h

Make array of arrays and result is joined array :)