Accessing the digits of a number in JavaScript

Let now we store not a number in quotes in a variable, but just a number. In this case, an attempt to access its individual character will return undefined, since such an access only works for strings:

let test = 12345;
alert(test[0]); // shows undefined

let's convert our number to a string to solve the problem:

let test = String(12345); // string
alert(test[0]); // shows '1' - everything works

Suppose now we want to find the sum of the first two digits:

let test = String(12345); // string
alert(test[0] + test[1]); // shows '12' - concatenates like strings

Let's add the function Number so that the characters are summed as numbers:

let test = String(12345); // string
alert(Number(test[0]) + Number(test[1])); // shows 3

I remind you that a problem of this kind will arise only with summation. When multiplying, for example, conversion to numbers can be omitted:

let test = String(12345); // string
alert(test[1] * test[2]); // shows 6

The number given is 12345. Find the sum of the digits of this number.

The number given is 12345. Find the product of the digits of this number.

The number given is 12345. Rearrange the digits of this number in reverse order.