JSFiddle - React, Tailwind, and code Playground

HTML

<div id="my-div">test</div>

CSS

#my-div{
    display: none;
    position: absolute;
    left: 150vh;
    top: 0;
}

JavaScript

$.fn.vhLeft = function(property , unit, adder){
    var el1 = this.get(0), el2 = document.createElement('div');
    
    $('body').append(el2);
    el2.style[property] = 1 + unit;

    var px1 = parseFloat(window.getComputedStyle(el1).getPropertyValue(property).replace(/[^0-9\,\.\-]/g, '')),
        px2 = parseFloat(window.getComputedStyle(el2).getPropertyValue(property).replace(/[^0-9\,\.\-]/g, '')),
        tot = Math.round( px1 / px2 );
    
    if (adder) {
        tot = tot + (adder);
        el1.style[property] = tot + unit;
    }
    
    $(el2).remove();
    
    return tot;
};

var vh = $('#my-div').vhLeft('left','vh');
console.log('Initial value : ' + vh);
var vh2 = $('#my-div').vhLeft('left','vh', 12);
console.log('new value : ' + vh2);