How to send a large amount of data faster ?

Please post the Arduino code for comparison.

Here is another approach:

Try moving the new UintArray(chk) to a Global scope

//Global scope
var n = 4, chk=5*1024;
var tdata=new Uint8Array(chk);

function onPageRequest(req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  var t=getTime();
  res.on('drain',function() {
  print("n=",n,"t:",(getTime()-t).toFixed(3),"sec");
  if (n===0){ res.end();
   print("n=",n,"t:",(getTime()-t).toFixed(3),"sec");
  }else {  
   res.write(E.toString(tdata));  
    n--;
   }//end else
  });//end opr
 }//end function

IP=  192.168.1.9
null
Wi-Fi Connected
n= 4 t: 0.008 sec
n= 3 t: 1.097 sec
n= 2 t: 2.214 sec
n= 1 t: 3.447 sec