Why this code results in NaN?

Question

var x = 4;
var y = 5;
var d = 4 + z;
var z = y - x;
var c = x+z+d+y; alert(c);

Answer 1

DO NOT PUT CODE IN THE TITLE SECTION. Put it in the description part or link it.

Answer 2

"z" has not been defined when using it in line 3, 4 + undefinded is not a number.
In strict mode, this code may not work.
edit: Seems to work in strict mode.

Answer 3

Keep in mind. Code in JavaScript is read and executed from top to bottom, following the order in which it appears in the script.

Answer 4

You're right about "var" hoisting and the result should be 14 not 15.
Ok so when you initialised "d", z is "undefined". Just one line above "d", z has no numerical value. From the philosophical POV, the value of d is the same thing as
var d = 4 + sololearn
or
var d = 4 + lion
It doesn't make any sense in numerical term and therefore isn't a number, so z must be initialized to a number first
z = 0;
var d = 4 + z;
var z = y - x;

Answer 5

at the time "d" is declared, "z" is not defined yet, resulting in undefined, this makes any calculation on it worthless (still results in undefined)

Answer 6

Probably using Z before it's defined.
But var accepts hoisting so the result should result 15.

Answer 7

OK Lisa

Answer 8

Strict mode?

Answer 9

Umer
In 3rd statement you didn't even defined z variable and using it for sum. You have define it later.
And what you even mean by strict mode?

Answer 10

Try using
alert(int(c));