Practical usage of if-else conditions in JavaScript

The variable month contains some number in the interval from 1 to 12. Determine what time of the year this month falls (winter, summer, spring, autumn).

Given a string consisting of characters, for example, 'abcde'. Check that the first character of this string is the letter 'a'. If so, print 'yes', otherwise print 'no'.

A number is given, for example, 12345. Check that the first character of this number is 1, 2 or 3. If so, print 'yes', otherwise print 'no'.

Given a three-digit number. Find the sum of the digits of this number.

Given a 6-digit number. Check that the sum of the first three digits is equal to the sum of the second three digits. If so, print 'yes', otherwise print 'no'.