# Euler Project Problem 2 JavaScript

Just solved Euler Project Problem 2 using JavaScript and I would like to know how I could improve my code. I do think it looks good, but you never know.

### Problem Statement

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...


By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

function fibonacci() {
var a = 0, b = 1, count = 0;

for(var sum = 0; sum < 4000000;){

sum = a + b;

a = b;
b = sum;

if(sum % 2 == 0){
count += sum;
}
}
return count;
}

console.log(fibonacci());

• Are you sure you're getting the correct result? You start with different numbers and your ending isn't spot on, although the latter doesn't seem to influence the outcome. Dec 1, 2021 at 23:03

With a bit of fiddling I come to this code:

function fibonacci() {
let s = t = 0, a = 1, b = 2;
do {
s = a + b;
a = b;
b = s;
t += s & 1 ? 0 : s;
} while (s <= 4000000);
return t;
}

console.log(fibonacci());


It is pretty much the same as yours with a few difference:

• I start with a = 1, b = 2 as per instructions, but this means my result is 4613730 and not 4613732.
• let will do for the variables, because they are only used in the block they are in, but since that is the same as the function var is fine too.
• I also follow the instructions where it says to: "not exceed four million", this includes four million.
• I prefer the clean look of the do { ... } while loop. This also means I don't have to initialized the sum.
• There's nothing wrong with your (sum % 2 == 0) check, but mine is visibly shorter. Normally I don't care about that and would prefer yours because is easier to read.

I think the real art is to do this with less operations.

• Would you mind explaining to me how to read the t += s & 1 ? 0 : s; line? Dec 1, 2021 at 23:45
• @fabinfabinfabin Sorry, yes that's a bit esoteric. It's easier to read when written as: t += (s & 1) ? 0 : s;. First the s & 1 bit, see the answer here: How to determine if a number is odd in JavaScript. The other bit, ... ? ... : ..., is using a ternary operator, basically a short way of writing "if .... then .... else ....". Dec 2, 2021 at 0:27
• Minor nitpick - you probably want to declare your "s" variable, so it's not global. "let/const s = a + b". Dec 2, 2021 at 18:41
• @ScottyJamison Yes, that's a good point, I'll edit my code. Dec 2, 2021 at 19:00