[Vuejs]-Update the height of a DOM element by adding a resize event listener

As the error message is trying to tell you, clientHeight is a read only property. You’ll probably want to modify the style.height property, but keep in mind clientHeight includes the padding. Try getting the element style using Window.getComputedStyle() and getting the width from there.

However, you can actually achieve this without using any JS at all: http://www.mademyday.de/css-height-equals-width-with-pure-css.html