Split a number to individual digits in javascript using basic methods

Your error is here:

for (var count = 0; count < number.toString().length; count++)
  arr[count] = number % 10;
number = Math.floor(number / 10);

Only the first statement is included in the for loop, the second only runs after the for loop ends. You need braces around both statements so both run on each iteration.

for (var count = 0; count < number.toString().length; count++) {
  arr[count] = number % 10;
  number = Math.floor(number / 10);
}

But you'll still get the wrong result because you reset the limit for count on each iteration. Set it once at the start.

var count = 0;
var arr = [];

function Split(number) {
  if (Math.floor(number / 10) > 0) {
    for (var count = 0, countLen = number.toString().length; count < countLen; count++) {
      arr[count] = number % 10;
      number = Math.floor(number / 10);
    }
  }
  return arr;
}
document.write(Split(2345));