在Angularjs指令中从滚动容器div的顶部获取元素位置

Question

I have a simple structure div named scrollContainer with overflow-y:scroll rule and an inner larger div called inner .

In the inner div I have some texts and an input. On the input I have an attribute directive called getPosition applied, which should return on scroll event the exact position of the input relative to the top of scrollContainer .

This is what I need:

Here is the sample angular app: https://codepen.io/neptune01/pen/vapmLQ

As you can see, tried with offsetTop and other dom properties, but I couldn't find anything that would result what I need.

Answer 1

I would recommend using a combination of getBoundingClientRect() and the current scroll position to accomplish this like so:

let outer = document.getElementById('scrollContainer');
let inner = document.getElementById('inner');

let outerTop = outer.getBoundingClientRect().top + (window.scrollY || window.pageYOffset);
let innerTop = inner.getBoundingClientRect().top + (window.scrollY || window.pageYOffset);

let difference = innerTop - outerTop;

The reason you wouldn't just subtract outer top from inner top in the first place and ignore the scroll position is because on the off chance that you are scrolling while the calculations take place you could throw off the offset, as getBoundingClientRect() only takes into account the distance from the edge of your view to the element, while the scrollY shows the distance from the edge of your view to the top of the document.