JSFiddle - React, Tailwind, and code Playground

HTML

<input type="file" id="myFile" multiple="" />
<div id="filesize"></div>

JavaScript

var input=document.getElementById("myFile")
input.onchange = function(){
  var file=document.getElementById("filesize")
  var fz=0
  for(var w=0; w<input.files.length; w++){
    fz+=input.files[w].size
  }
  file.innerHTML='Your file(s) size: '+fz+' bytes'
}