javascript – Calculate real value of line-height

I try to access the line-height of html elements with js, using this method:

let myElement = document.querySelector(".myElement");
let lineHeight = window.getComputedStyle(myElement, null).getPropertyValue("line-height");

the returned value is 0px, but it’s not true.

How can I calculate the REAL value of line-height with JS? It’s not even font-size value.