The Javascript logical and ( && ) operator is used to group values or sub-expressions where the left and right operands must both evaluate to the same result. It makes good sense if you replace the characters ( && ) with the word "and" when you see that symbol sequence in scripts to get a mental grasp on it.
(value && value && value && etc...)
Here is an example evaluating string data. This script is ready to perform a check to make sure all values are present before the program can continue.