A CodePen by first-developer. Compute window size on resizing - Code use to compute window size when the browser is resizing

index.html

<div class="m"></div>

script.js

var windowResize = function(fun){
  var oldresize = window.onresize;

  window.onresize = function(e) {
    if (typeof oldresize == 'function') oldresize(e);
    fun(e);
  }
};

var res = function (e) {
  console.log([e.srcElement.outerWidth, e.srcElement.outerHeight]);
  var h = $(".m").outerWidth();
  console.log("Div width ", h);  
};


// jQuery version
/*$(window).on("resize", function(e) {
    console.log($(e.target).width());
  });*/

windowResize(res);

style.css

.m {
  display: block;
  width: 100%;
  height:20px;
  background-color: #000;
  box-sizing: border-box;
}