Comming from php, I noticed something in javascript that I found pretty wierd - how the the logical or operator || behaves.

In php, the expressions on boths sides of the or operator is being casted to a boolean. So

 false || true  // true
 0 || ''        // false
 '' || 0        // false
 null || "Hey!" // true

In javascript, however, if the first expression is truthy, it returns it, otherwise it returns the second expression

 false || true  // true
 0 || ""        // ""
 "" || 0        // 0
 null || "Hey!" // "Hey!"

Hmm. Doesn't that behaviour seem familiar? It does! It just how the php ternary shorthand operator works

"" ?: 0 // 0
0 ?: "" // ""

This i quite handy! Especially because javascript dosen't support the shorthand ternary.

Sometimes you want the php behaviour thought. How can you solve that? You simply need to convert the expression to a boolean yourself. That can be done in several ways. Here are a few:

Boolean("" || 0) // false
!! ("" || 0)     // false
!! "" || !! 0    // false

Conclusion

This gave me a real head scratch a while back, as i got some unexpected resuilts. I hope this short article might help another confused developer venturing from php to javascript :)

Ps. The same non casting behaviour goes for the logical and (&&) operator. Read more about it here