'JS array in array string

i have arrays in arrays like these

x[0][A,B,C]
x[1][D,E,F]
x[3][G,H,I]
x[4][J,K,L]
..
.
.
x[n][x,y,z]

in javascript how to get all possible string concatenations like ADGJ,ADGK,ADGL,ADHJ,ADHK,ADHL n so on

tried with for loop in for loop but no luck so far

any ideas ?

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