在div中从mouseclick获得x和y位置

I made a function that should add an item on the position I clicked inside a div. Now the problem with this function is, every time I click, it takes the x & y position of the document, not the x & y position inside the div. So what I actually want, is that the top-left corner of my div should give x=0 & y=0, but I don't know if this is possible? And I guess there is another way to do this..I made a function that should add an item on th