JSFiddle - React, Tailwind, and code Playground

by Castrolol

HTML

<input type="file" id="file" /><button id="b">click</button>

JavaScript

function getFileSize(inputFile){

    var size = -1;

    if( inputFile.files[0].size ){
        size = inputFile.files[0].size ;
    }else if( window["ActiveXObject"] ){
        var myFSO = new ActiveXObject("Scripting.FileSystemObject");
        var filepath = inputFile.value;
        var thefile = myFSO.getFile(filepath);
        size = thefile.size;
    }else{
        //so entrará aqui caso for IE6, 7 ou 8
        //e as diretivas de segurança impedirem 
        //o activeX
    }

    return size; //em bytes, divide por 1024 para kb e assim por diante
    
}



var f = document.querySelector("#file");
var btn = document.querySelector("#b");
btn.addEventListener("click",function(){
    debugger;
    getFileSize(f);
});