'2017'.split('');

function getNumbersSum(num){
  var result = 'num'.split('');
  alert(result);
}
getNumbersSum(2017);

function getNumbersSum(num){
     return num.toString().split('').reduce(function(a, b) {
         return +a + +b;
     })
}

var n=12345;
alert((''+n).split(''));

function getSumNumber(num) {
    var sum = 0, tmp;
    while (num) {
        tmp = num % 10;
        num = (num - tmp) / 10;
        sum += tmp;
    }
    return sum;
}

alert(getSumNumber(2610));

var n = 2017;

alert( eval(n.toString().split('').join('+')) );


alert( eval(n.toString().replace(/\d/g, '+$&')) );

function digitSum(y) {
    let sum = 0, x = String(y);
    
    for (let i = 0; i < x.length; i++) {
        sum += Number(x[i]);
    }
    return(sum)
}

// if alert(digitSum(123)), output is 6.