Javascript && operator behavior in chrome's V8

Question

As I'm writing a javascript interpreter I need to implement some basic functions. I was playing around a bit in my Chrome console I discovered this strange behavior in js. How can I interpret what is js doing in this particular case?

Thanks

Answer 1

Javascript's && operator returns the left part if it can be converted to false, otherwise returns the right part.

So in both cases you are getting the expression on the right (since neither 012 nor true can be converted to false). For the first case, true, and for the second case, 012.

Since 012 is octal, you are getting 10 output, which is the base-10 representation of octal 12

I can't find a better link for a source, so I'll quote this one (it's not V8 specific, but should do): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators

Logical AND (&&)

expr1 && expr2

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.

(bold is mine)

Answer 2

The way I interpret the && and || operators is like this:

a && b = a ? b : a;

a || b = a ? a : b;