Question

on my quest to learn and improve my JavaScript I came across a script that has a switch / case statement and I noticed some variables are incremented using ++ with the variable before the ++ and then some variables have the ++ after the variable. What’s the difference between these? Here’s an example of what I’m trying to explain notice the m and y variables.

 switch(f){
        case 0:{

            ++m;
            if(m==12){
                m=0;
                y++;
            }
            break;
        }
        case 1:{

            --m;
            if(m==-1){
                m=11;
                y--;
            }
            break;
        }
        case 2:{

            ++y;
            break;
        }
        case 3:{

            --y;
            break;
        }
        case 4:{

            break;
        }
        }

Answer 1

++i returns the value of i after it has been incremented. i++ returns the value of i before incrementing.

When the ++ comes before its operand it is called the “pre-increment” operator, and when it comes after it is called the “post-increment” operator.

This distinction is only important if you do something with the result.

var i = 0, j = 0;

alert(++i);  // alerts 1
alert(j++);  // alerts 0

One thing to note though is that even though i++ returns the value before incrementing, it still returns the value after it has been converted to a number.

So

var s = "1";
alert(typeof s++);  // alerts "number"
alert(s);  // alerts 2, not "11" as if by ("1" + 1)