# Intermediate Algorithm Scripting: Sum All Odd Fibonacci Numbers- explain pls

can you guys explain to me what’s happening on that line of code
` a = [b, b=b+a];` because i’m still new to javascript . and thats why i couldn’t understand what that line of code is doing ??

``````
function sumFibs(num) {
var a = 1;
var b = 1;
var s = 0;
while (a <= num) {
if (a % 2 !== 0) {
s += a;
}
a = [b, b=b+a];
}
return s;
}
console.log(sumFibs(4));
``````

User Agent is: `Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36`.

Challenge: Sum All Odd Fibonacci Numbers

That’s really convoluted way to assign at the same time `a = b` and `b = b + a`. To `a` is assigned first element (with index `0`) of the array `[b, b=b+a]`, while b is being reassigned to `b = b + a`.

This can be written more clearly in few ways. For example:
`[a, b] = [b, b + a];`
or with using another variable:

``````let temp = a
a = b
b = b + temp;
``````
2 Likes

thank you for explaining that !