Question

I have been using MDN Docs – Logical Operators as a frame of reference to understand the logical AND operator.

I have understood most of these code examples especially the first 4 as shown here:

a1=true && true       // t && t returns true
a2=true && false      // t && f returns false
a3=false && true      // f && t returns false
a4=false && (3 == 4)  // f && f returns false
a5="Cat" && "Dog"     // t && t returns Dog
a6=false && "Cat"     // f && t returns false
a7="Cat" && false     // t && f returns false

However I am having issue understanding a5, a6 and a7.

I am failing to understand how the two strings a5="Cat" && "Dog" are evaluating to true && true returns Dog

I am also failing to understand why the string “Cat” is evaluating to true as part of a6=false && "Cat" // f && t returns false

Answer 1

First of all lets look at a5:

a5="Cat" && "Dog" 

Which returns dog, the mdn-docs states that AND(&&):

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.

Since a non-empty string can’t be converted to false, it will return dog, if you change the order of dog and cat, it will ofcourse return cat.

In a6 false, is false and thus it returns false because of this:

Returns expr1 if it can be converted to false…

In a7 cat is true and thus it goes on to the next expression which is false, and thus returns false.

…otherwise, returns expr2