Noticed my mistake...
I must change "Return" with "break" and also add

target_durch = target_durch/targets.length;

I want to repair every structure that they have nearly same hitpoints.

First i tried this:

                var target_num = 0;
                var target_durch = 0;
                for(var i = 0; i < targets.length; i++){
                    target_durch += targets[i].hits;
                }
                for(var i = 0; i < targets.length; i++){
                    if(targets[i].hits <= target_durch){
                        target_num = i;
                        return;
                    }
                }

I wanted to get the average actual hitpoints from every structure and than set the structure what need to repair first. The Creeps don´t walk with this code. With static target, the creep will only repair one target and a wall with a lot of hitpoints... well you know what i mean.

I think i made an stupid mistake with the code. Also "traget_durch" means "traget_average"