In JavaScript, && is the logical AND operator. It operates on a set of boolean operands and returns true only if all the operands are true, otherwise it returns false. The operator can also be used with non-boolean operands, but it is still considered a boolean operator since its return value can always be converted to a boolean primitive.

The && operator evaluates the operands from left to right and returns the first falsy value encountered. If no operand is falsy, the latest operand is returned. The operator is short-circuiting, meaning that if the first operand is falsy, the operator stops and returns the original value of that falsy operand; it does not evaluate any of the remaining operands.

The && operator can be used in a shorthand way to check if something is not null or undefined before doing something else. For example, x && foo() is equivalent to if(x){ foo(); }.

There is also a logical AND assignment operator, &&=, which only evaluates the right operand and assigns to the left if the left operand is truthy.