Problem with E.toString

Here is the test code

//xtest.js 26 Jan2018
// trying this on a Pico
//try changing the value of chk

var n =100, chk=23*1024;
var tdata=new Uint8Array(chk);
var i;
for(i=0;i<1024;i++){
  tdata[i]=0x30;
  tdata[i+1024]=0x31;
}//next i

function xsend(a){console.log(n,a.length);}

function test(){
while (n){
  xsend(E.toString(tdata));
  n--;
}
}//end test


test();

Here is the output

 1v95 Copyright 2017 G.Williams
>100 23552
99 23552
98 23552
97 23552
Uncaught Error: Field or method "length" does not already exist, and can't create it on undefined
 at line 13 col 16
console.log(n,a.length);
               ^
in function "xsend" called from line 17 col 26
  xsend(E.toString(tdata));
                         ^
in function "test" called from line 1 col 6
test();
     ^
=undefined
>

Similar problem on ESP8266 running Espruino, but different array sizes to get it to run at all.