While loop validation

Question

I came across a question that asks to find the GCD (Greatest Common Divisor) of two numbers.
I wrote a code for it and it worked fine but I also checked the solution to look more efficient ways to write it. The solution looks like this:

function gcd_two_numbers(x, y) {
if ((typeof x !== 'number') || (typeof y !== 'number')) return false;
x = Math.abs(x);
y = Math.abs(y);
while(y) {
var t = y;
y = x % y;
x = t;
}
return x;
}

console.log(gcd_two_numbers(12, 13)); // outputs 1

I don't understand understand most part of this code but what's most confusing is the while loop. I know it executes it's code when the condition passed to it is true. But in this case the condition passed to it is y (i.e while(y)), where y = 13. How does this validates? And also y doesn't increments or decrements inside the loop so I don't understand how the while loop iterates.
Secondly I don't how they could find the gcd with the code in the loop.

Answer 1

*Tag the language also..

In js, anything other than 0 is evaluated as true..
And empty string, none, undefined, 0, null... are treated as false..

So a number 13 (not 0) is true there..

x=12,y=13

In while loop,

t=13
y=12%13=12
x=13

t=12
y=13%12=1
x=12

t=1
y=12%1=0
x=1

While loop y=0 stops..
Output x=1

Answer 2

Oh great. Thanks for your explanation Jayakrishna🇮🇳 . I understand it now.

Answer 3

You're welcome..

Answer 4

Jayakrishna🇮🇳 can you also explain this code. The same question. This finds the gcd of more than two numbers using an array to input the numbers.
I wrote the code, it worked fine but it's nothing like this.

function ex9(x, y){
if(!y) return y === 0 ? x : NaN;
return ex9(y, x % y);
}

function gcd(arr){
var n = 0;
for( var i = 0; i < arr.length; i++){
n = ex9(arr[i], n);
return n;
}
}
console.log(gcd([3,15,27]));
console.log(gcd([5,10,15,25]));

Answer 5

function ex9(x, y){
if(!y) //when y=0 it returns x otherwise it call this same function recursively by x=y, y=x%y
return y === 0 ? x : NaN;

return ex9(y, x % y);
}

function gcd(arr){
var n = 0;
for( var i = 0; i < arr.length; i++){
n = ex9(arr[i], n); => calling function ( 3,0), (15,3), (27,3) returned value is assigned to N which is new y next
return n;
}
}
console.log(gcd([3,15,27]));
3,0 =>0%3=0
n=3
15,3 =>15%3=0
n=3
27,3 => 27%3=0
Return x=3 finally
console.log(gcd([5,10,15,25]));
5,0 => 0%5=0
n=5
10,5 =>10%5=0
n=5
15,5 =>15%5=0
n=5
25,5 => 25%5=0
Return x= 5 finally Eddy Ricchy