Euler Project Problem 2 JavaScript

Question

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());

Answer 1

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.