Why avoid increment (“++”) and decrement (“--”) operators in JavaScript?

Question

One of the tips for jslint tool is:

++ and --
The ++ (increment) and -- (decrement) operators have been known to contribute

Answer 1

Consider the following code

    int a[10];
    a[0] = 0;
    a[1] = 0;
    a[2] = 0;
    a[3] = 0;
    int i = 0;
    a[i++] = i++;
    a[i++] = i++;
    a[i++] = i++;

since i++ gets evaluated twice the output is (from vs2005 debugger)

    [0] 0   int
    [1] 0   int
    [2] 2   int
    [3] 0   int
    [4] 4   int

Now consider the following code :

    int a[10];
    a[0] = 0;
    a[1] = 0;
    a[2] = 0;
    a[3] = 0;
    int i = 0;
    a[++i] = ++i;
    a[++i] = ++i;
    a[++i] = ++i;

Notice that the output is the same. Now you might think that ++i and i++ are the same. They are not

    [0] 0   int
    [1] 0   int
    [2] 2   int
    [3] 0   int
    [4] 4   int

Finally consider this code

    int a[10];
    a[0] = 0;
    a[1] = 0;
    a[2] = 0;
    a[3] = 0;
    int i = 0;
    a[++i] = i++;
    a[++i] = i++;
    a[++i] = i++;

The output is now :

    [0] 0   int
    [1] 1   int
    [2] 0   int
    [3] 3   int
    [4] 0   int
    [5] 5   int

So they are not the same, mixing both result in not so intuitive behavior. I think that for loops are ok with ++, but watch out when you have multiple ++ symbols on the same line or same instruction