javascript - file input does not update except in Chrome -

i have local program writes json object file javascript can pick data , process it. file selected using <input> object:

<form id = "getfiles">     <input type = "file" multiple id = "files" /> </form> 

with following js function setinterval repeat every 300ms. however, when file changes, google chrome reloads file , processes new content; have manually reselect file on page in ie 10 , firefox 20.

function speaktext()  {     var thefile = document.getelementbyid('files').files[0];     var lastchanged = thefile.lastmodifieddate;     var reader = new filereader();                     reader.onload = function(event)     {         var lcd = document.getelementbyid("last_change_date");         if (!lcd)         {             var spanlastchanged = document.createelement("span");             spanlastchanged.id = "last_change_date";             spanlastchanged.innertext = lastchanged;             console.log(lastchanged);             document.body.appendchild(spanlastchanged);         }         else         {             // compare lastchanged last_change_date             var last_known_change = date.parse(lcd.innertext);             // var last_known_change = date.parse(thefile.lastmodifieddate);             if (last_known_change !== date.parse(lastchanged))             {                 console.log("something new since " + lcd.innertext);                 var filecontent = event.target.result;                 var commands = json.parse(filecontent);                 handlejson(filecontent);                 lcd.innertext = lastchanged;             }         }     }     reader.readastext(thefile, "utf-8");  } 

firefox , ie doing right thing per spec: file objects associated file input supposed immutable snapshots of file @ point when file object created. it's known bug in webkit/blink store reference file's data, mutating data change file object sees.

in fact, webkit/blink behavior privacy bug: when user selects file in file input, giving web page permission read data of file at time, not future versions of file! why spec written is.