Counts the number of carry operation in an addition of two numbers

carryOperationsCounter.js

function numberOfCarryOperations(x,y) {
    var xs = x.toString();
    var ys = y.toString();
    var cary = 0;
    var operations=0;
    var xCurrent;
    var yCurrent;

    while (xs.substr(xs.length-1) || ys.substr(ys.length-1) ) {
        yCurrent =ys.substr(ys.length-1);
        xCurrent = xs.substr(xs.length-1);
        xs = xs.substr(0, xs.length-1);
        ys = ys.substr(0, ys.length-1);

        var sum = cary + Number(yCurrent) + Number(xCurrent);

        if ( sum >= 10) {
            cary = Math.floor(sum/10);
            operations += 1;
        }

    }

    return operations;
}

tests.js

console.log(numberOfCarryOperations(123, 456) === 0)
console.log(numberOfCarryOperations(555, 555) === 3)
console.log(numberOfCarryOperations(900, 11) === 0)
console.log(numberOfCarryOperations(145, 55) === 2)
console.log(numberOfCarryOperations(0, 0) === 0 )
console.log(numberOfCarryOperations(1, 99999) === 5)
console.log(numberOfCarryOperations(999045, 1055) === 5)

Counts the number of carry operation in an addition of two numbers