Counting the number of occurrences of each parity among a range of adjacent integers

sumdigits.js

let start = 1;
let end = 123456789;

let evenCount = 0;
let oddCount = 0;


for (let i = start; i <= end; i++) {
    if (isEven(sumDigits(i))) {
        evenCount++;
    } else {
        oddCount++;
    }

    if (i % 1000 === 0) {
        console.log(100 * ((i - start) / (end - start)) + " % complete!");
    }
}

console.log("Even: " + evenCount);
console.log("Odd: " + oddCount);


function sumDigits(number) {
    var str = number.toString();
    var sum = 0;

    for (var i = 0; i < str.length; i++) {
        sum += parseInt(str.charAt(i), 10);
    }

    return sum;
}


function isEven(n) {
    return n % 2 == 0;
}