Question

43

What's the difference between ++i and i++ in JavaScript

rated 0 times [ 50] [ 7] / answers: 1 / hits: 15326 / 13 Years ago, thu, june 16, 2011, 12:00:00

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;

        }

        }

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answered 13 Years ago trevionbronsonr · Accepted Answer

++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)