javascript - How to get placement coordinates of an absolutely positioned element relative to another? -

i can't seem find on github here go:

suppose have dom element parent contains position: relative , element child contains position: absolute , child of parent, how can go getting coordinates [top, left] child element [relative parent] given placement string? (i.e. "top left", "top middle", "bottom right", , forth... ?)

ideally, this:

var coordinates = getrelativecoordinates({   el:           child        // child element contains "position: absolute"   relativetoel: parent       // parent container contains "position: relative"   placement:    "top left"   // "top left" || "top middle" || "top right" || "right top" || etc... });  console.log(coordinates); >> {top: "-100px", left: "0px"} 

"when position set absolute, element removed normal document flow—that is, no longer takes space , may overlap other elements. also, top , left properties can used absolutely position relative top-left corner of nearest enclosing element position property isn’t static, or relative document if no such enclosing element exists." - http://eloquentjavascript.net/13_dom.html

then need compute: if know .width , .height properties, can compute different places adding top left amount of width or height.

ex. (top middle) = ((parseint(child.style.left) + parseint(child.style.width)/2) , parseint(child.style.top)) (x, y)

note parseint used number out "px".

you need write out each possible location computation this. store them array [left, top] or in object {left: , top: }.