Why is Javascript giving result as Number instead of True/False for expression? [duplicate]

Question

I was rambling with JavaScript code in my application today when I observed something strange.

var someVar = 25; 
var anotherVar = 50; 
var out = (anotherVar == 50 && someVar); 


console.log(out) // outputs 25 and not true or false;

Any idea what's happening?

Answer 1

As stated on MDN's Logical Operators page, the && operator:

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

In your case, expr1 (anotherVar == 50) is true (not false), so it returns expr2 (someVar), which is 25.

It doesn't return true or false because expr2 isn't a Boolean value.

The ECMA-262 Specification notes:

The value produced by a && or || operator is not necessarily of type Boolean. The value produced will always be the value of one of the two operand expressions.