I was browsing Google Code when I chanced upon this project called JSpeed - optimization for Javascript.

I noticed one of the optimization was to change i++ to ++i in for loop statements.

Before Optimization

for (i=0;i<1;i++) {}



for (var i = 0, j = 0; i < 1000000; i++, j++) {

    if (i == 4) {

        var tmp = i / 2;

    }



    if ((i % 2) == 0) {

        var tmp = i / 2;

        i++;

    }

}

var arr = new Array(1000000);

for (i = 0; i < arr.length; i++) {}

After optimization

for(var i=0;i<1;++i){}

for(var i=0,j=0;i<1000000;++i,++j){if(i==4){var tmp=i>>1;}

if((i&1)==0){var tmp=i>>1;i++;}}

var arr=new Array(1000000);for(var i=0,arr_len=arr.length;i<arr_len;++i){}

I know what pre and post increments do, but any idea how does this speeds the code up?