en.javascript.info/1-js/02-first-steps/12-while-for/2-which-value-while/solution.md

The task demonstrates how postfix/prefix forms can lead to different results when used in comparisons.

1. From 1 to 4

   let i = 0;
   while (++i < 5) alert( i );
   

   The first value is i=1, because ++i first increments i and then returns the new value. So the first comparison is 1 < 5 and the alert shows 1.

   Then follow 2,3,4… -- the values show up one after another. The comparison always uses the incremented value, because ++ is before the variable.

   Finally, i=4 is incremented to 5, the comparison while(5 < 5) fails, and the loop stops. So 5 is not shown.

2. From 1 to 5

   let i = 0;
   while (i++ < 5) alert( i );
   

   The first value is again i=1. The postfix form of i++ increments i and then returns the old value, so the comparison i++ < 5 will use i=0 (contrary to ++i < 5).

   But the alert call is separate. It's another statement which executes after the increment and the comparison. So it gets the current i=1.

   Then follow 2,3,4…

   Let's stop on i=4. The prefix form ++i would increment it and use 5 in the comparison. But here we have the postfix form i++. So it increments i to 5, but returns the old value. Hence the comparison is actually while(4 < 5) -- true, and the control goes on to alert.

   The value i=5 is the last one, because on the next step while(5 < 5) is false.