Javascript doubt

Question

what is the output of this code and why, thanks
var a = 1;
var b = 2;
var d = "8";
var c = d + (a = b + 1) - d;
alert(c);

Answer 1

The expression:
d + (a = b + 1) - d;

First, parentheses boosts precedence, so let's first handle the part within parentheses:
(a = b + 1) // a become 3

Outside the parentheses we see two operators with same precedence. + to the left, and - to the right. We handle the left part first, then on to the right, because they have same precedence.

A + operator between a string and a number behaves as string concatenation, so when we deal with this:

"8" + (a)
"8" + 3 // + act as string concatenation

Here we have "83" from concatenating "8" and 3.

Lastly, we deal with the - operator:

"83" - "8"

Wait, string can be concatenated with + operator, but there is no overload for - operator of string class. So JavaScript convert the two string into numbers before proceeding. And then we have this:

83 - 8

Voila! it turned out the output was just that, 83 - 8. Then we tell JavaScript to alert us that value , 75.

Hth, cmiiw

Answer 2

thanks I understood perfectly

Answer 3

You're welcome, glad if it helps 👍