|| and &&

&& is guard operator aka "logical and", and || is default operator "aka logical or", we normally see the code like the following

if ( condtion1 && condition2) { } if (condition1 || condition2) { }

&& means, If first operand is truthy, the result is second operand, else result is is first operand. It can be used to avoid null reference.

if (a){ return a.memeber; } else { return a; } //this is the same return a && a.member

|| means, if first operand is truethy, then result is first operand, else result is second operand. It can be used to fill in default value like the following

var last = input || {}; //{} is default value