Long boolean expression

Question

Why the console shows "2" and "false" in this expressions?

var a = '' || 0 || 2 || true || false;
var b = 3 && true && false && null;
console.log (a,b);

Answer 1

You got those results because it's logical comparison here, using logical operators && and ||, if you take a look at MDN Specification of Logical Operators, you will see that:

Logical OR (||): Returns expr1 if it can be converted to true; otherwise, returns expr2. Thus, when used with Boolean values, || returns true if either operand can be converted to true; if both can be converted to false, returns false.

Logical AND (&&): Returns expr1 if it can be converted to false; otherwise, returns expr2. Thus, when used with Boolean values, && returns true if both operands can be converted to true; otherwise, returns false.

So in your case:

For the first expression:

var a = '' || 0 || 2 || true || false;

It will return 2 because it's the first oprand that's evaluated to true.

And for the second one:

var b = 3 && true && false && null;

It will return false as one of its operand is false.