2-Even_Fibonacci_numbers.js

/**
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.

*/

let arr = [1, 2];
let max = 4000000;
let len = arr.length;
let sum = 2;

while (arr[len - 1] < max) {
    let next = arr[len - 1] + arr[len - 2];
    sum += next % 2 === 0 ? next : 0;
    arr.push(next);
    len = arr.length;
}

console.log(sum) // expect 4613732