javascript: get css prop value with unit [duplicate]

Question

my code like this:

#image_1 {
   position: absolute;
   top: 3vw;  
}

My try: http://jsfiddle.net/z8k6t3fb/1/

I want get '3vw'

Is it possible ?

Answer 1

You can iterate document.styleSheets, .cssRules, if .selectorText matches element selector, select rule from .style property

window.onload = function() {
  var element = document.getElementById("image_1");
  var prop = "top";
  var styles = document.styleSheets;
  for (var j = 0; j < styles.length; j++) {
    var rules = document.styleSheets[j].cssRules;
    for (var i = 0; i < rules.length; i++) {
      if (rules[i].selectorText === "#" + element.id) {
        console.log(rules[i].style[prop])
      }
    }
  }
}

#image_1 {
  position: absolute;
  top: 3vw;
}

<div id="image_1">hello</div>