<div id="progressbar">
  <div id="loading"></div>
  <div id="value">0%</div>
</div>
<br />
<button onclick="isProgressing()">Click Me</button>

#progressbar {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: flex-start;
  width: 100%;
  background: lightgrey;
}
 
#loading {
  width: 1%;
  height: 25px;
  background: green;
}

#value {
  position: absolute;
  right: 10px;
}

var i = 0;
function isProgressing() {
  if (i == 0) {
    i = 1;
    var elem = document.getElementById("loading");
    var val = document.getElementById("value");
    var width = 0;
    var id = setInterval(frame, 1);
    function frame() {
      if (width >= 100) {
        clearInterval(id);
        i = 0;
      } else {
        width++;
        elem.style.width = width + "%";
        val.innerHTML = width  + "%";
      }
    }
  }
}